Not sure why retrofit is sometimes not available.

[samuraipoet]

Here's the situation: I have some free necrodrone units I got from a quest. This is pretty late in the game, so I've updated the basic necrodrone design a few times. I want to retrofit the free ones I got, but the game won't let me.

I know you have to have the dust and metals you need, and I know you have to be in your own territory. Are there are more conditions that need to be met?

Is there a rule that says you can't upgrade free units? it's the same with the free forager units I get from my proliferator's parasitism capacity.

[DragonFang]

Free units can't be upgraded. Same way merc units from the market aren't upgradeable. So if I had to guess quest reward units are concidered mercenary unitys from the market.

[Ra'ri]

I can confirm this. Looks like you can only retrofit units you actually built in one of your cities (plus your starting units).