When insuring my Anniversary bass the first decision I needed to make was whether to insure at full replacement cost - if lost, I would have Alembic make an exact replacement, or to insure at street value (which is always subjective). I decided on full replacement cost as the difference in premiums wasn't all that great, your results may vary.
You could contact Alembic for assistance in determining costs for new instruments then and now if you needed something official when dealing with your insurance carrier. Probably a good idea for the JPJ. Their custom quote generator could get you in the ball park. If you're seeking full replacement costs I doubt original sale values would mean much.
I contacted my carrier and asked how they determined value (ebay histories, dealers, etc.) for total loss, damage/repairs, etc; I figured it was good to know how the game was played. It was helpful. Might be worth a call.
I'm not sure if it would have any bearing on the rates if the basses are classified as pleasure/luxury items or if you're gigging with them as a tradesman might, I didn't ask.
Many years ago I lost my Ric when my house was robbed. The insurance replacement money was far lower than what I paid for it, even after just a few years. Sour lesson, and it's a difficult argument to win with an adjuster.
There have been a couple of Club threads that have asked similar questions, could be worth a search.
Mike