Don't know much about nettles.
Never tried preemergent on garlic mustard.
There tends to be a long lasting seed bank of garlic mustard. The key tends to be pulling up and removing the garlic mustard plants or else spraying them before they set seed.
Sounds like you need some aggressive natives like goldenrod and jewel weed. Maybe also some ferns, wood asters and other natives that can multiply themselves in the woods. In spots that are sunnier and wetter you could try joe pye weed.
What kind of trees do you have? If you have norway maple or ailanthus they might be contributing to the lack of success of more desired plants.

Here is a link that might be useful: Garlic Mustard

At our local wildflower society meeting last month a restoration ecologist told us that garlic mustard seedlings cannot push up through leave mulch. He has found that it grows mostly in areas where wind the natural leaf cover away or where human activities like hiking trails, mountain bikes and so on have diminished the leaf cover. He said slow to decompose leaves like maple, beach and oak spread over garlic mustard patches soon eliminate it.

will gladly take any suggestions of native aggressive plants that like zone 4 shade/partial to choke out the nettles.

Regarding the garlic mustand - I deal with this plant all the time - it is an aggressive bienniel weed.

I use different methods depending on where it is in it's life cycle.

For instance, if it's small stuff just pushing up you can usually use roundup (glycophospate)and then mulch right over it. And then spot spray for stray seedlings. You may have to do this more then once.

But it sounds like you have a well established patch which means that there's quite a bit of seed stored up in the soil. I'd say in that case, hand pulling should be a last resort, because disturbing the soil will only cause more to sprout. But if you go this route you must be sure to dig up the entire plant or it will reshoot from the remaining roots.

If it's a large area sometimes I'll even actually wait until the plant begins setting seed because it is actually easier to pull the whole plant (roots and all) by hand because it's near the end of it's life cycle and is in a weakened state. Then I spray anything else that hasn't been pulled.

However, if you can't hand pull or spray at least cut the tops of the seedheads and dispose of in the trash - do not recycle them in the compost pile. This will cut down on new generations.

I have Garlic mustard sprouting up all over through my woods...mostly beech trees with English Ivy, and in some places through vinca. I find it has no problem multiplying and rising up through the leaves and ground cover. (I'd like to get rid of the ground covers as well!) I am pulling it before it flowers, but it crosses into the neighbors section of woods so I think it will be an endless battle.

Why do you have a hate for nettles. Its a good spring green, one of the first to come up and one of the most nutritious.

I don't "hate" nettles, but I have 2 acres of woodland and want more native variety. I know nettles are also natives, so I am leaving them alone on about 1/4 acre. I now have a granddaughter that I want to share the woods with and nettles are very painful.

Gosh do they ever hurt when you touch them. They're almost as bad as hornet stings - the pain is residual. I've had them hurt for several days afterward. Native or not I can't say I blame you for wanting to reduce the population somewhat. They're are some natives like biennial primrose, ragweed, nettles and water hemlock that while they do deserve a place in our local ecosystem I would not overly encourage to spread too much.

My mother used to say a good homemade remedy after being stung is to wrap the affected area with Doc. It's that big leafed weed with a long taproot that is common in waste areas.

You can certainly eat the nettles, or use them as a hair rinse, but you can also eat the garlic mustard, as it really is a mustard. I think that the seeds of GM lie underground,and when they are exposed to light, they germinate. I am still pulling, after loosening soil, and trying to pull blooms off before they can seed.

The garlic mustard is popping up already. The good news was that while searching for it, I discovered the hepatica is also blooming in the woods. It makes me even more determined to control the garlic mustard. I read somewhere this winter that all gardeners should carry a small spray bottle of baking soda & water to spray on a stinging nettle attack. I also read that rubbing chamois on it will remove the stinging hairs.