Terps: I think that you may be crediting crabgrass with being a thinking creature, which it is not. Or you may be thinking that Pre-M "prevents" germination, which it does not - even though the name is "pre-emergent". Crabgrass seeds germinate when there is adequate moisture (think April showers) and proper soil temperatures. The Pre-M does not "delay" the germination, and the crabgrass seeds can't really "outlast" the Pre-M's effectiveness. The Pre-M works by preventing root formation after the grass has actually germinated. With no root system, it wilts and dies before you even see it. No second chances, no waiting for the Pre-M to lose it's effectiveness. It's germinated and dead. The only crabgrass that makes it is if the conditions for germination don't happen before the Pre-M barrier breaks down. If you want to bet that we might not get 60 degrees and wet weather before 90 days from now, than put down more at the beginning of Summer. I'm saving my money to use the additional Pre-M in very late Summer to prevent the Poa Annua germination period (which will overwinter and be NEXT Spring's headache).

I have read to put it down when the crocus bloom. I'm in zone 5 and my perennials are all starting to come up already. Not sure about annual weeds, but I think the window is fast closing on putting down pre-emergent unless you are quite a bit further north than we are. We use corn gluten meal, and while the jury is still out on its effectiveness, we already put it down a week or two ago.

I'm in Greenville SC, so not too different of a climate zone. Fall of 2014, I had a similar situation as yours, but much worse. Sodded Bermuda with a massive number of broadleaf and grassy weeds (maybe about 3x what your pics show). Battled those down all of 2015 and did a lot of reading and research to figure out what my weeds were and what was the best way to make the next year better. I went with an application of Prodiamine, which is the same active ingredient in Stonewall. I had planned to do a split application, but decided the 2nd app wasn't needed because of our mild temperatures. So, it was about 0.2oz/1000 sqft applied Sept 12th 2015 with my sprayer. I went with the liquid for better coverage. This was my first time using it, and I am very impressed with the results. I have almost no broadleaf weeds so far this year *except* right around the edges of the lawn where I probably didn't spray well. In your 2nd pic, I believe the weed on the right is a Carolina Geranium, and the middle one is some sort of thistle (Creeping Thistle?). Not sure about that left one, however, Prodiamine should have fairly consistently knocked out those first two. That makes me think either the application wasn't enough, wasn't timed correctly, or wasn't spread evenly. So, if I had to suggest a change for next year, you might try the liquid instead of the granules, and apply about a month earlier. Target Sept 15th for our area, but with Prodiamine, it lasts a good amount of time in the soil, so earlier won't be a bad thing.

Solve the equation by selecting your "m" and it will result in the dosage amount per gallon which would cover 1000sqft. This is a common misconception. The amount of carrier (water) per ksf is a function of the sprayer volume, not a pre-determined thing, which is why spraying requires calibration. What you do is you mark a 10x10 section of driveway , take your sprayer and a timer, and see how long it takes you to spray that 100 sq ft section. You then take a large measuring cup and spray into it for the same amount of time to see how much water it used for 100 sq ft. Multiply that by ten and now you know how much water to use per thousand sq feet. My backpack sprayer with the fan nozzle puts out 1.3 gallons per ksf. The round spray nozzle puts out 0.7 gallons per ksf, but can be adjusted. If I'm trying to apply prodiamine to 3000 sq ft with the fan spray at a rate of 0.5oz per ksf, I would add 3.9 gallons of water to the sprayer and 1.5oz of prodiamine. If I'm going to do it with the round spray nozzle I would add 2.1 gallons of water and 1.5 oz of prodiamine. The amount of water will vary based on nozzle output and calibration. Calibration has to be done every time to ensure correct application.