x and check on units??

[Blathergut]

When I go into the editor, I've made a bit of a map. But when I go into the units section, some have green check marks and some have red x's. What are these?

[Erik2]

Many units have (first) available/expire dates.
Units with red x's are not available for purchase when you're playing the game. Their available/expire dates are 'outside' the scenario start date.
You can still deploy them in the editor and they will show up in the game.