The question is why did I suggest using a few sollie sd's to refurbish. It's not about money because a star system is going to lose money on refurbishing an SD. Now, they could take some of Manties or Grayson obselote regular SD's it does not matter. Granted it would be cheaper to refurbish the Grayson/Manticoran/Erewhon SD's than it would be a captured Solly SD. In the end, a star system is not going to save that much money on using a Grayson/Manticoran/Erewhon SD. What they are going to learn is the technical skills that are needed to build SD's. What equipment is needed etc...etc...etc...
Refurbishing presupposes that they have something to refurbish
with. That means having a source of parts and facilities with mechanical support to do refurbishing in. This is not some tiny amount of pocket change for a star nation. It is a massive investment across the board in multiple fields and industries. One has to be able to
produce the replacement parts, otherwise the whole exercise is not possible.
Let's take Marsh or whoever as example when building SD's. (Now Marsh really does not have the population to support a yard that can build SD's) They refurbish a couple of SD's and decide to build a couple of SD podnaughts with the technical skills they learned by refurshing some old SD's. As a result, they decide to build modular podnaughts that are put together. They then grow the armor in place after the podnaughts are built are built or nearly completed. This process might save money or it might save time in construction. What if Grayson or Manitcore could save 6 to 8 months in building podnaughts by having another star system build their own yards and they discover a better way to build podnaughts. For most star systems, they are going to build a standard yard because they know the process works. Their are only a few systems that have the technical skills and the more importantly the money to build SD podnaughts.
Refurbishing an old solid-cored SD designed for energy range combat is not going to provide a lot of experience in developing new hollow-cored SD(P)s. It took significant redesign time with many revisions to make the podnought design work. A navy without any institutional experience in building capital ships just is not going to crap out a working SD(P) design easily.
I also take exception to your optimistic estimate of how much time you can knock off SD(P) construction. Both Manticore and Grayson were producing SD(P)s as fast as physically possible at around 20 months, and even that took some seriously risky shortcuts. There is no more fat that can be cut from the meat there. It certainly cannot be done by some minor Verge entity which has no experience building warships.