User blog comment:Nausiated/Project 11/61: Mission Impossible!/@comment-11836-20140727035100/@comment-61022-20140729103240

Some crossovers take place on Earth-7642 as a lot of the early intercompany crossovers (such as Superman/Spider-Man, Batman/Incredible Hulk and even the X-Men/Teen Titans crossovers) happened in a "shared universe" where both Marvel and DC's respective characters existed. This universe also contained pretty much every other cross-over that is in a "same universe" context (like Punisher Meets Archie, the X-Men/Wildstorm crossover etc.)

It's only been more recent that crossovers involving crossing dimensions have been a thing, and as such, are considered part of Earth-616 continuity (the Superman/Silver Surfer crossover being one of them) the most recent run of Marvel Handbooks specify which ones in given characters biographies (all be it the names of the other company's characters are not used, instead they use an easy to identify general description) The universe crossing thing has been somewhat standard practice since the Marvel vs DC crossover, although it's not always the case. The most recent run of Marvel/Top Cow crossovers happened in a "shared universe" (which again is likely Earth-7642 since it's the "catch-all", it started off as something that the guys at the Unofficial Appendix did to kind of lump all those crossovers together, and Marvel officially accepted that logic when they hired the Appendix guys to do the most recent run of handbooks)