I think many production bikes of the 1960's and 1970's used parts dated year #(N-1) for a year #N bicycle. So, when I have a choice in parts, I try to collect the #(N-1) parts for my #N year bicycle. I imagine that sometimes a bike with year #(N-1) used #(N-1) parts, but only at the end of the year, maybe.
Examples (to support this thesis) in my collection include a mostly-original 1974 raleigh pro (missing the hubs), an original 1974 raleigh international, and an all-original 1974 Schwinn Paramount. I also have an all-original 1970 raleigh international. The first three bikes had PAT 73 parts on them when I acquired them, and serial numbers for 1974 framesets. The 1970 bike had campy parts consistent with 1970/1969.
In general I only worry about campy parts, but you might look at http://www.vintage-trek.com to find out how to get the dates for other parts (i.e. weinmann brakes and japanese stems, bars, and derailleurs.)
I especially don't care about things you can't see without taking apart the bike or looking with a microscope, i.e. axle cones, BB spindles, BB liners, inner tubes, spoke heads, axles, washers, brake clamps, microadjusting seatpost bolts, etc.
I try not to care about wear items like chains, axle cones, tires, tape, brake cables, brake cable housings (lined housings are safer), and brake pads (fresh modern pads are almost always superior to fresh NOS pads.)
If you acquire original wear items like a Sedis chain you should probably just save it for display - and use modern stuff for riding the bike.
I live near some very steep hills. Once upon a time I could not stop with some original campy brake pads. After that incident I keep all my keep brakes tuned up with modern parts to preserve my body and to preserve the bike for posterity.
I like to protect original parts as follows
- brake lever covers, made of rubber or plastic - fenders (to preserve the paint and decals) - crank arm plastic protective decals (www.vcgraphix.com) - clip-on chainstay protector - saddle cover (makes leaning the bike against a wall easier)
- Don Gillies
San Diego, CA, USA