I have a boxed copy of System 7.0, and like you I can't find anything in the EULA allowing redistribution, however I do believe they must have released it as free at some point - I have a CD titled "Nautilus Intro V7" that came with our LCIII (which we bought brand new back in 1993) thats full of shareware, freeware and PD software from the era, and it has images of both System 6.08 and System 7.0. System 7.01 was also released as free at some point. Then in 1999, 7.5.3 was released as free. However, 7.1, 7.5.0 and 7.6 were never free.

As for your question regarding backup copies of software you are licensed for - unfortunately it is kind of iffy, since short of scanning and posting an EULA, there's no way for us to be certain that you are licensed to run the software (and you typically won't get an EULA with an old Mac anyway, after all this time), and...well...we don't want to get sued.