Originally Posted by
Scooper
The easiest ways to tell a 1973 P13-9 from a P10-9 frame are the way the rear brake cable is routed on the frame's top tube (the P13-9 uses three chrome plated Campy cable clips, while the P10-9 uses two top tube braze-ons), and the P13 doesn't have front fork and rear dropout eyelets for fenders/racks while the P10-9 does.
Just to add to Stan's comments: Only the post-'71 P13's are virtually guaranteed to be eyeletless, unless they are from a special order build. The pre-'71 P13's were generally fitted with eyelets, though some were not; I had a Paramount replacement fork (fork had no serial #) dating from prior to 1967 without eyelets. I also have the fork off of B802, a 1968 fork with a Vagner crown, and that is also sans-eyelets.
-Kurt