The Big Book of Amiga Hardware lists three different versions of the Amiga 500 rev 5 motherboard which it names Type 1, Type 2, and Type 3. Were the changes made only to simplify manufacturing, or were there any real-life differences between the three that makes one of these better in some way than the others?
It is hard to find authoritative information about the differences between the various A500 PCB revisions but aside from what is already signalled in the Big Book of Amiga Hardware they essentially differ by the position and types of the jumpers which control how the expansion memory can be used.
These jumpers serve to specify whether the expansion memory should be used as slow RAM or chip RAM and their position change between boards revisions. For some models, in addition to modifying the jumpers it is also necessary to draw wires between various points of the board.
Alas, this information does not seem to be collected in a single place at the moment.
Update (2017/12/23): An initiative to reverse engineer Amiga PCBs and visualize them in schematics form is currently ongoing and is visible at http://amigapcb.org. Their beta site covers one of the A500 revision so it might be of interest to you.