Another good point worth remembering is that some playfields that have been repro'd actually have some improvements over the originals.

I think when some originals were done 30 odd years ago there may have been a tendency at times to "rush through" the playfield so as to get the machine on the market and maybe the art department couldn't spend as much time on the PF as they would have liked.
 Maybe Nino or Tony who are very knowledgable on pinball history would know better than me on this, but I do know from reading CPR's updates on playfield and BG printing that they have incorporated some improvements over the originals.
Some recent examples would be Eight Ball Playfield and Fathom Playfield where they used a deeper blue for the inserts.

Fathom initial run had some issues because I believe the films that CPR obtained were in fact not the final product. They worked off a prototype. Some playfield lettering was placed incorrectly. What CPR strive to do is have the original colors. NOS playfields have faded, so the Blue became a Greenish color. Their repro should be faithful to the original.