Huge caveat: IANAIPL and this advice is worth no more than the sum total of what you have paid me for it - ie. nothing.

Is the copyright more associated with the module(s), or with the distribution?

My understanding has always been that copyright refers to anything written. Since modules within a dist might be broken apart later the copyright should be associated with each module - even more correctly with each file. If you have a separate LICEN[SC]E file in your dist you may find for example that it has an embedded copyright notice which far predates anything else in the dist. I have my templates set up so that each script or module which I create includes a separate copyright notice in the source.

Your other questions cannot really be answered by me with any authority. If this concerns you greatly the best thing to do would be to seek the advice of a qualified legal expert in the field (and then report back here, of course). Alternatively, the OSI or EPO or EFF (or other TLA) may have guidance documentation?