Instead of having ships "assigned", which is an idea I have never liked, couldn't we just set the shiplist at a particular time and leave it as for the duration of the server. Sure the turns would click by, but the shiplist would never change.
Say, the shiplist is set to 2268, and those ships available would show in the shipyard. Nothing new would show up. What you have at that time stamp would be all you are going to get for the duration. You can create an early, mid, or even late era feel for the whole time.
Agave