I would think that time and repetition would smooth things out. It's hard to put an exact figure on how long, it probably varied wildly depending on the factory, the weapon, etc., but figure by, maybe, 3055 you'd probably have things down to a routine, worked out bugs in the systems, etc.- after all, production was ramped up as much as possible to meet the Clan threat, so you've had plenty of practice!
Note too that in situations like the Streak missile system, you wouldn't start researching how to build a four or six pack if the Streak SRM-2 still isn't coming out right, so by the late 3050s at the most I'd think things are smoothed out- and even that would be a surprisingly long time.