Where I REALLY run into problems is with die varieties/die marriages. An C-1 1809 Classic Head Half Cent is an R-4 or R-5 depending on your source. An C-6 1809 Classic Head Half Cent is an R-1. The value difference is at least a factor of 10x-20x. Fortunately I've been retaining my receipts in the last 10 years or so and can get values from them.
And so does everybody else. That's because values for these are driven more by personal emotion than they are by normal determining factors. My point here is that values for these will be all over map because of who exactly happens to be buying at the time.
Please remember that for insurance purposes you want to make sure the policy covers full replacement cost. If you use historical cost, that's all you get paid out. And that won't replace the item. If you use retail cost, that's what you get paid out and if it's not the bog-standard 1916D Mercury Dime, that won't replace the PCGS MS66+* CACd coin you actually have. Oh, and while they'll happily write you coverage based on your estimates, when it comes time to make a claim, they'll fight you on it. With FRC you can tell them to replace it. For any serious claim it will involve lawyers and you are better off having had a professional numismatic appraiser involved from the start (but that costs you).
Like I've said, anything significant in my collection (>$100) is slabbed. Therefore I consider that as having been done by a "professional numismatic appraiser".
Many think that, but it's not the same, not even close. Which is why I suggested that you determine value the way I did. It's about the only way there is to cover contingencies. That said, when push comes to shove, you could have 3 or 4 different professional appraisals done and on record, but the only appraisal the insurance company will count is the one they have done. None of yours will matter all, no matter who did them. edit - When it comes to insurance claims, it's a whole lot like what happens when you submit a coin to a TPG for grade guarantee. The TPG, and only the TPG, will be who determines what the value of that coin actually is. You will have no say in the matter at all.