I was thinking (uh-oh). Classic scopes that are listed at a bargain price would naturally tend to sell faster than scopes priced higher. And some would sell very fast, and if the seller deletes the listing* before someone on this forum finds it and posts it here we never learn about it. This could mean that the average selling prices of vintage scopes are lower than the average prices of scopes posted here.
For items with a Make Offer option, the SOLD price noted is often not the price it actually sold for. When a seller accepts a lower price than that listed, only the listed price shows to others. There is no usable data in those instances other that what the seller's desired price was, not what it actually sold for.