I'll work my way back down the comments in responses
7.1.2 was created to introduce the PPC line; separately, 7.1.2P was released -- and oddly, it wasn't just released for Performas -- it was released for the Quadra/LC 630 series as well. The documentation seems mixed on this; sometimes it says that 7.1.2P was for Performas and 7.1.2 was for PPC and for Quadras -- but the actual build/restore images and DevCDs all had the Quadras getting 7.1.2P.
Mac OS 7.5.4 was released to GM, but there was a problem in Apple's own automation pipeline that resulted in some of the localized GM releases missing parts of the software. As a result, the German 7.5.4 was actually pressed to CD and distributed, and the US 7.5.4 went up on Apple's FTP site for a few hours (I remember receiving an announcement email at around noon, grabbed my copy just before 1, and they'd pulled it by 2 PM).
7.5.5 was because they didn't want to replicate the fiasco of 7.5 Update 3.0, 7.5.3, 7.5.3r2, 7.5.3r2.1 and two 7.5.3r2.2 versions. Easier to just call 7.5.4 a bust and re-version to 7.5.5 once the automation was fixed.
Anyway, back to my original question, which is specifically about the 7.0.x series.
@chelseayr is likely correct, and Apple was using the numbers internally as placeholders (I suspect for international versions that ran out of time) and they never got released. The known releases were:
7.0 GM
7.0.1
7.0.1.1-Z (International)
7.0.1P (for Performa 200)
7.0.4-SV (Swedish localization)
On top of that, after 7.0.1P but before 7.0.4 went out, we had System 7 Tune-Up, System 7 Tune-Up 1.1 and System 7 Tune-Up 1.1.1 (with Tuna Helper) all of which could patch any OS in the 7.0.x series, adding patches via extensions instead of just updating the OS and cranking the number. All three versions of Tune-Up added a bullet after the version number to indicate they'd been applied.
So specifically, I'm looking for anyone who has actual information on what went on with 7.0.2 and 7.0.3; all I've got right now is the above running theory that these numbers were reserved for localizations and were overtaken by System 7.1 (which, considering the release date of 7.0.4, makes sense -- the only reason 7.0.2 and 7.0.3 would have been released is if the 7.1 localization team was significantly delayed, like what happened with the Swedish team).
Even when System 7 Tune-Up 1.1 was released, people were throwing around 7.0.2 and 7.0.3 as versions, but they usually meant 7.0.1 with one of the Tune-Up extensions installed, and it doesn't show up anywhere in Apple's own documentation or official versionings.
Then again, we already know that Apple wasn't above making things up as they went along, giving us the System Software 0.1, 0.3, 0.5 and 0.7 OS naming convention years after the fact as a way to group combinations of system software back before they started tracking full software distributions. But someone who worked at Apple must know what really happened with 7.0.x.