Not all PX10's are created equal. For any given year there are 6 distinct lug/fork crown combinations. There are 2 fork corwns you'll find, the more typical Nervex style and the less typical UO8 style. Aside from a shortage of crowns I haven't come across any plausable reason as to why one bike has one style while another one doesnt. There are 3 lug work combinations you'll find, full fancy Nervex, fancy Nervex head and seat lugs with a seamed BB shell and last combination will have NO fancy lugs. A bike with NO fancy lugwork isnt a bad thing as long as it has a Nervex fork corwn and its a '74 PX10LE. The PX10LE model, which is 1 step above the PX10, has plain lugwork. The LE model wasnt available until '74 so the lugwork hierarchy pertains primarily to pre-'74 models although the regular '74 PX10 would fall into the 6 groups as well.

The 6 combinations are:

Nerves fork crown with:
Full fancy Nervex lugs
Fancy head and seat lubs with a seamed BB
NO fancy lugwork

UO8 style fork crown with:
Full fancy Nervex lugs
Fancy head and seat lubs with a seamed BB
NO fancy lugwork

Some bikes have riveted serial number plates while others dont. As best as I can tell bikes with seamed BB shells have no plate while seamless (Nervex?) have a plate.

That being said, aside from the frame being a small size and having the most desireable of lug/crown combinations I have no explanations as to why it sold for so much.