I figured I'd run some ideas past you all and see what your lines of thought might be on this issue.
According to TA7, it suggests that fleet research and development occurs at the various depot systems and that once a ship is debugged (hopefully) it is put into production. After these ships serve in the navy, and they reach a time where they are superceded by better ship designs or perhaps upgraded with better technology, the obsolete ships and their systems are essentially retired.
What is perhaps interesting however is the thought that such technology is not lost as such, but tends to be archived. While we may not be able to retool current factories to produce cars from the 1940's in an exact replicated form, we do have records of how those cars were manufactured and likely even have on record somewhere, the actual design plans for the making of said vehicles - at least for those that were preserved.
This brings me to the next question. If the Imperial Navy hands off its obsolete ships to the Imperial Reserves, might it not also hand over the designs for obsolete ships that are TWO tech levels below their own to any world that desires them for local production? This way, the subsector navies can save perhaps some money in Research and Development, the Imperial Navy can keep cutting edge information out of the hands of the local navies so that they can't sell them to enemies of the Imperium (or have them stolen by spies) as well as permitting the higher tech worlds to sell information as a commidity?
What all do you think? The reason I ask is because some of the older TL 10 designs for world may be newly produced by certain worlds such that functionally, they are NEW ships, but that they are no longer top of the line. This benefits the Imperium in other ways. For example, the Imperium higher tech worlds can produce the replacement parts that lower tech worlds need for repairs of their ships. When repair ships need to repair battle damage, fabrication shops can purpose build replacement "jury rigged" parts built to specs they already have.