Not to demean the knowledge or abilities of people on this forum, but mushrooms are really not something to mess around with, nor would I personally be reassured or at all comfortable with a positive ID from anyone based on a single picture.
I went out collecting several times with a university prof, am still extremely cautious, and have known two people, the prof being one of them, that have made themselves ill through misidentification.
You may have a different tolerance for risk, though.

I've never seen a mature shitake with a curled-up cap. Be careful. Didn't the place that sold you the plugs tell you how to identify them??

Considering the risk of serious illness or likelyhood of death with certain mushrooms (not to mention the risk of being tormented by evil leprechauns), I would definitely take this question to someone who would be liable for their answer....

You'll get as good advice from a needlepoint forum about mushroom ID as you will here at a vegetable gardening forum. I wouldn't trust advice you get from here about that, and if I knew a lot about mushrooms, I wouldn't be posting advice for someone asking here.

I agree, even with a good mushroom identification book it is difficult to get a positive ID. Doing a spore print can help a lot with identification. For most edible mushrooms there are usually look-a-likes that are in-edible or even poisonous.

That being said I have picked and eaten wild Oyster, Chanterelle, Morel, Hen of the woods, and Lobster mushrooms on my property and have not died yet :)

The rounded uper edge margins of your mushrooms, size, shape, placement on the log, fact they all look similar before fully expanded and those light fuzz spots ringing the upper caps all look right.

I have grown shiitake with flat or very slightly upcurled tops, when they get past prime. Your younger caps look right. I've seen and grown them at times quite light too or darker than normal too.

Shape and color can vary with strain, moisture level when expanding, light intensity, growth medium and/or temperature. Low light, and on the dry warm side, is when I've seen them even lighter than yours, especially when grown inside on sawdust.

Critical to its scientific naming AND determining the correct ID of Shiitake (Lentinus edodes) is the gill shape. Note that your mushrooms do indeed have a long irregular sawtooth-like wave pattern on the top edge of those cream colored gills. It's so distinctive I can easily see it in your photo.

This gill edge is unusual and can be easily seen when you view gills from the side. Each sawtooth gill differs in alignment a bit as you look across a set of gills. That is one of the key attributes of being a Lentinula (old name = Lentinus).

There is another common North American species with this sized mushroom and this gill edge pattern. It can look similar in color and basic shape from a distance, but is distinctly different up close. Lentinula lepidus also grows on wood. It is not poisionous but doesn't taste good. It's a great wood degrader though, with an interesting US history.

Before they started using preservatives effectively on wooden railroad ties, L. lepidus was known as the "train wrecker". This is for the carnage that it left behind by the railroad ties that it rather quickly rotted.

Buy some fresh shiitake at the store and compare it's gills with your next Shiitake grown. Shiitake also has a quite distinctive odor. Slight hints of aromatic spice and an acrid sulfer-like compound, reminding me of some cabbages when you bruise them and let them sit

Having said the above however stiil never eat a mushroom until you are totally sure!

There's some bad unforgiving players out there, especially those found growing wild on the ground.

Look up "Amanita" and "Destroying Angel". Beware of any fungus with a basal "Deathcup" that rips away from the cap. And what looks like an edible Puffball may instead be a juvenile Amanita!

So when collecting common Puffballs commonly found growing on the ground, cut each in half before eating. Sure all Puffballs are often said to be edible. But Puffballs do not have gills plates forming inside the cap, which can be easily seen in a cross cut section.

Good explanation, Gary. When I started harvesting Shiitake mushrooms I looked at the mushrooms- they all looked similar; I looked where they grew from- adjacent to where I placed plugs when logs were inoculated. Based on those criteria alone I tasted a few.

I have a book on wild mushroom identification but we're not talking about wild mushrooms here. If you plant a row of any vegetable and the row has resulted in a crop that looks like a vegetable you expected then I would feel fairly confident eating that vegetable.

Do very gad you survived (but wasn't worried because you wrote back). I'm told there's few really bad mushrooms fruiting up in the air on wood logs, that get the size and appearence of a gilled mushroom up. Of course you don't want to discover a new one!

The Amanitas on the ground (above buried tree roots) are quite nasty. No sign after eating, until many hours later. The victim starts losing water from both ends to try to self flush the toxin, but it is too late. If one eats below a certain totally dose, they might be able to save them they can be hydrated enough.

Above a lethal dose the science gets interesting. Too much of the liver auto digests and between that and inability to hydrate the person, there's no saving them.

Cells are always turning over protein and remaking it. The literature I read said that the the toxin stops protein production by liver cells. Cells then autodigest. Less liver less chance to pick more mushrooms. Happy to have no first hand experience with this.

Many inoculation sites in shittake cultivation on logs are used to help ensure that it wins out over other wood degrading fungi. Note however that Shiitake can pop up quite a distance down the log from where the plugs were introduced it into the log.

The mycelium runs from the that perfect placement of pegs down the sapwood zone and under the bark running pretty fast through the open plant vascular tissue. It's after the easy to get carbohydrates, in the attempt to secure them before other other fungi. Then can it compete quite well, slowly degrading the other wood for energy source.

You can get more nitrogen (in protein and amino acids) in the mushrooms harvested over time than in the original log!

No this is not alchemy! It just suggests that nitrogen fixing bacteria got in there and were eaten by shiitake or external nitrogen was tranported in. At times shiitake mycelium runs out of the ends into the soil or leaf litter zone and it can pump nutrients back.

In the spring or wet fall periods I've lifted logs and some had a nice patch of leaves (1-2' diameter) sticking to log as you lift it! Tricky fungus is harvesting what it needs. It can compete a little at soil level because it's powered by a lot of log behind, which it can degrade to get energy.

In a faster closed nutrient system, such as in sawdust culture you must add grain or other nitrogen sources to get good mushroom yield. Luckily the mushrooms are more valuable than the grain.

Are you just letting rainy weather make mushrooms or stimulating production 3 to 4 times a year by submerging logs under water and then restacking for fruiting? The idea is to let shiitake degrade wood a few months, then stimulate fruiting and repeat. At least some dim light is needed to grow shiitake indoors. This is because light is needed to initiate fruiting. And then it gets more complex.

In nature on a log, the mycelium knows where to pop up. Light and lowered carbon dioxide levels are required to fruit, and bark extractives are stimulatory to fruiting. This how shiitake can choose to fruit on the log surface, rather than futility inside the log. Light, an increased rate of carbon dioxide loss, and bark are all at the surface.

The expanding mushroom then uses gravity, light and perhaps carbon dioxide or surface water dehydration sensing? to know where to aim the cap and get the its spore holding umbrella up into a better place to cast spores to the wind. Rather than just let them get washed down right under the fungus on the ground that umbrella cap helps ensure it. The spores are trying to be deposited on newly fallen trees during fall, winter, spring weather. I think a chain saw works "more better".

Nature is neat huh?

Some of the above mushroom expansion phase needs more research.

I did some of the early work in an earlier career on initial light trigger, carbon dioxide trigger, and bark stimulators. This was way back in the later half of the 70's through early 80's. Much fun.