FWIW, I had my 59 TR3A insured with Mercury. Since it was a daily driver, there was no way to qualify for "collector" insurance like Hagarty or JC Taylor or Grundy offer. Also normally stored outdoors.
Basically I stated a "not to exceed" value for the car, which is what my premium was based on; while any actual payment would be for actual damages. The car was pretty rough when I signed up, so I only stated $8k.
Few years ago, I was the cream filling in a 4-car chain collision. Took some doing to find a shop that would even give an estimate on repairing it; estimate was $12k.
To determine my car's value, Mercury found four "comparable sales", meaning TR3As in similar condition that had sold within the previous year. I saw the list, and could have argued that those cars were not comparable and/or provide counterexamples if I wanted to (but they were). The average of those actual sale prices was $8800, more than my "not to exceed" amount; so they just cut me a check for $8000 and let me keep the wreck/salvage. Since my freshly rebuilt 4-synchro OD gearbox (with the beefed up TR6 main housing) was intact; along with several other go-fast goodies, I feel I made out quite well.
Of course, my other choice was to turn down Mercury's offer and pursue the guy that hit me directly. No doubt it was his fault as I and the other two cars in front of me were fully stopped before he hit us; and he even admitted to the CHP on the scene that he was not watching the road. But I doubt I could have gotten more than $10k from his insurance, so I chose to accept Mercury's offer.
YMMV and all that, but I'm happy with Mercury and they still carry my insurance (house and car).