Sounded like you did know actually, it was more a general notice to others that getting a valuation is one half of the equation. Unless you do what you are doing, it has zero legal use in a claim.
In your case, if you do that and the price plummets during the year, the insurer is obliged to still pay out the estimate you gave as they set their premium to that.
It's a proper minefield but you are for sure doing it right. Plenty don't.
Some market values they set are nuts.
I had one legal battle on the basis of ok find me another....I actually won it.
I now ONLY do agreed value on precious toys.
Run of the mill I take the same risk millions do.