If there are just little 'sockets' where buds should be, that stem is dead.
If buds exist but just aren't coloring and swelling, give one a gentle flick. If the bud pops off --> not good. If the bud stays on, just be patient.
If the bark seems thin and is dark brown to black the cambium likely died and that stem likely is dead.
They were outside tucked in a corner of my deck all winter. I pressed my nail into the trunk and all are soft live wood. So I don't think they are dead but very shocked it was their first nebraska winter too.
When the bark turns black, it's not a good sign. It might be they took a beating from the cold and some branches will die off. Alive buds should show no wrinkles, i.e. smooth surface and some kind of light color, reddish or another depending on the species. Usually not black or grey but I don't know all the species...
You seem to have different species, some of them grafted.
There are at least a thousand registered Japanese maple cultivars: some are earlier than others.
I don't know what the weather is like in Nebraska, but here, the winter has been very mild, and last week, we had unusually warm temperatures, up to 22° C (71,6 F) when it's supposed to be in the 10-15 range (50-59 F), and very sunny.
Maybe you have an 'Atropurpureum' of some sort, dark-red-leaved maple: mine have buds that are just beginning to swell. Same with the plain species (green leaves), but 'Little princess' has already opened up its leaves.
Once again, it depends on the weather conditions too: when we had 71,6 F here in the afternoon (and no night frost for weeks), I saw the snow storm on the east coast of the USA on TV. But here, it's foie gras and wine, and early spring.
Oh là là, la belle vie for zi maples
Too late to take pictures: it's 18:40 here, rather cloudy and the light is too oow now for good pictures.
This week might be our first without freezing at night. But our weather is very sporadic literally 73° Tuesday then down to 13°and snowing Thursday then back up again. I figured it being their first winter here it would throw them off a bit. But wasn't sure how much our weather can vary in a week would. As it seems I'll just have to wait a bit longer to see some new life. Even though a lot of trees and shrubs began swelling and opening weeks ago