It has been a few years since I grew any softneck, so I scrolled back through my pictures to see if there was any harvest date. I was shocked to see my New York White with full size bulbs harvested only the third of August. It was a warm year but also very wet, and some bulbs were past their prime already with the wrappers split open, although leaves remained green that whole season and couldn't be used to judge maturity at all.

One thing that has been consistent every year is that the porcelain scapes always come at the same time my gentians are blooming, usually in the middle of July, but this year both are emerging already due to the hot weather we had since late May. There is already some drying of leaves this time, and I watered all the garlic much more this year than any other, because it was so hot and dry.

So I'm wondering, for those who grow both hardneck and softneck, is there a way to gauge the softneck maturity by comparison to the stage that the hardnecks are at?

At least with the hardnecks, I know they are usually ready about two weeks after removing the scapes. Our harvest dates are very variable, and have been really late the past two cold years, but this one is shaping up to be early. IIRC, softnecks were ready about two weeks earlier than hardnecks? But perhaps that depends on the variety as well... IDK.

I think one should look at the remaining green leaves on the garlic plant. You want to harvest it when you see 4 green leaves remaining. Each leaf is a layer protecting the bulb. The more wrappers on a bulb, the longer it will keep in storage.

So when you see a plant with 4 green leaves left, carefully dig around the plant to inspect the bulb. Confirm that it has filled out ok. That is, you see a head of garlic with some ridges between each clove. If you don't see that, you would leave it in the ground a bit longer and inspect again. If you get to 3 green leaves remaining and the bulb hasn't changed, then you might as well just pull it.

I went out and counted the leaves, I think the '4 leaves' can work for the largest ones, some are smaller (due to being only year 2 from bulbils) so they only had 6 leaves to start with and have lost or are losing a couple. I'll just watch for those lower leaves to die down completely and then I'll try digging down to get a look at.
I'm not expecting full size bulbs on these, but Messidor is getting close (based on stem size and height).