There are several factors (out of which normal wear and missing rivets may be the two most important or otherwise the only two I know of) that may concur on the feel of a Model M.
On the other hand, I have a NIB 1401 and one 1986 0131 with 11 rivets missing. The 1930131 is crispier, more precise and has almost 0 ping. I got the 1401 first and was later surprised by the feel of the old, dirty 0131.
They both have black plastic plates on the interior. I was just wondering if there's anything special about the ones with beige/ivory plates.