Have you gotten this error?
When I first tried to load a world from modded minecraft 1.7.10 into 1.12.2, I got the following error: This save predates 1.7.10, it can no longer be loaded here. Please load in 1.7.10 or 1.8 first. Thus began a several month-long hacking spree, first to get this message to go away, and then to get the world in question, a world my wife and I had been recording videos in for several years, to not just load but load well...mostly. The program started out as a quick and dirty hack and got dirtier and hackier the more I realized how much work it needed to do. If I had known then what I know now, I probably would have made it a proper application. If there is sufficient interest, I may yet do so. Regardless, what I have so far may prove useful to others, so I'm creating a blog for it, where folks can express such interest and talk about the problem. FYI: the accepted wisdom is that the best/only way to load modded 1.7.10 worlds into 1.12.2 is to load them into intermedia...