I have read on the Profantasy forums, a must read I must say, about lost work due to noticing an error that is too far back for undo to reach.
Here is how I get around that.
After settling on what template I am going to use, I do a ‘save as’ filename_00001 make a few changes to the map, and then save as to filename_00002 and so forth.
That way if I suddenly realize, and I did this to myself more than once prompting this idea, that I went wrong on my map, and I need to go back 40 or 50 versions. With all of them saved as multiple maps, I can go back. It also allows me the chance to branch off in another direction if I am not satisfied with the mapping direction I am going in.
Of course, when I upload the maps, pngs and web pages to this site, the number on the end is gone. That way even if I wind up drawing over 200 map versions, the viewers never see that number on my site.