@Man Eating Duck, @GeekyGal, thank you both for the feedback.
Yeah, custom columns. I tried out 2 additional columns Edition and Title2 the other day, then went back to appending that info to Title because less than 300 books were affected, out of thousands, and I haven't had any pathlength problems yet (btw, that is on a Mac). I've been trying to avoid adding new columns. I've actually been looking for ways to reduce them. Also I've been trying to avoid complex template programming, which could solve the "which is which" issue regarding formats. Finally, I've been trying to avoid extra workflow steps, and reduce the number of steps.
I am aware that by bending over backward trying to keep things simple, I may actually be making things overly complex and shooting myself in the foot. So I'm also trying to miss my foot.
Disk space is cheap. That isn't the driver on the issue of keeping original formats or not. It is a major issue involving my basic strategy with Preferred Format and Original Format, which affects a lot of other things. The primary problem for me is confusion about which is master_fixed_best format, which is the original format, which is the temporary_generated_throw-away format. Without having extra workflow steps, extra columns, general program mode template programming, or anything adversely affecting performance. Keeping the database and booklist pretty, and reducing horizontal space for seeing formats at a glance in the booklist, are both minor factors in comparison to the confusion.
All downloaded books can be kept in an AddedToCalibre folder rather than deleted after Adding to calibre. That seems simpler than keeping incoming original formats in calibre, and seems to completely resolve the potential confusion, for me at least. Original formats are basically copies of the original downloaded books that were added into calibre. When I've had to resort to re-adding a book because I botched something, re-adding it from AddedToCalibre folder worked well. The book files in the AddedToCalibre folder are a bit different because they are not directly associated with the metadata in calibre, may have DRM, and may include multiple formats per title, some of which weren't Added, but those factors seem minor and the frequency is low for having to resort back to them to redo something, for me perhaps ten books a year or less.