Suppose you have a couple of slightly different designs of the same class that you want to work with. Using your suggestion of obsoleting all but one, you tell one of your older ships of that class to retrofit to the one you specifically left available. Shortly, thereafter, you have another ship of the same class that you want retrofitted to a slightly different spec. At that point, can you obsolete the first retrofitted design in favor of the second design without affecting the retrofitting of the first ship in progress or do you have to wait until the retrofitting of the first ship is totally complete before initiating the retrofitting of the second ship to the different design?
Once a retrofit order is issued, it *should* be possible to obsolete the design something is retrofitting to.
I have had some weird effect once, though: retrofitting a Small Space Port to a Medium design changed only the name of the design in that instance, the installation was still a very outdated Small design when finished - number of construction yards and everything else remained that of a Small port. When I tried to rectify the situation, the right-click retrofit menu showed only my current Large and Small designs. So somehow the game was assuming the retrofit had succeeded while it clearly didn't.
I can only guess how that came to pass, and it might be connected to obsoleting a design while a retrofit order was being performed, More likely it was a completely different issue. I am not even sure the design the Space Port was supposed to retrofit to was at any time obsoleted. I'd have issued a bug report, if there had been any information available at the time I discovered that mishap, but there's virtually nothing I have in hand.
So, that being said, I am generally cautious with repeatedly (un-)obsoleting a given design. For ships, I rather issue all retrofit orders manually via the ships and bases screen. I keep all current variants of a ship class unobsolted. There are usually at most two such variants. I (multi-) select what I want to retrofit to the same design in the list of military ships, and when I click the 'Retrofit' button, I select the desired design from the list. That's it.
< Message edited by sbach2o -- 12/22/2011 2:23:18 PM >