Yes! I did just what you’re asking a couple years ago when PanX first appeared. And you’re right to do it pre-Catalina as later you can’t, at least not without using something like Parallels to emulate earlier OSX versions. And trying to organize my conversions made my progress faster and less frustrating.
What you want to do is first identify (see below for how) all your old pre-Pan6 files, open them with Pan6 and save them, ideally to a different location, which converts them to the Pan6 format. Those can then be opened and saved as PanX files. With luck they just work, without they take some work. A few pre-Pan6 files, including some included in earlier Panorama versions, couldn’t be converted forward. But most converted easily and quickly, even with my 100s of Pan6 and earlier files. At least to where I could use PanX for the final adjustments.
I suggest using the Finder’s optional Tags to mark all your pre-Pan6, and separately your Pan6, versions so you can re-find them again easily if needed. You can make/manage/search whatever Tags you want via the Finder. No additional apps are needed for that although some are sold making their use easier. You can have multiple tags per file. I even made special tags for groups of files with similar conversion problems. Once I deciphered how to fix one such I could quickly find the rest and repeat the fix.
The key to finding older Pan files is to use the older way OSX, OS9, etc. kept tract of which documents belonged to which applications. Before the current “file extensions” Macs used
Creator Codes and
File Type Codes. The OSX file system still saves the old ones, but it, by itself, no longer lets you see them, much less still search for them. The solution is
Find Any File, $8 at the App Store. It still has that capability, albeit hidden. It initially offers a “Name” popup menu, from which you can pick other search criteria. Option clicking that offers a longer list, including
Creator Code and
File Type code. Clicking + lets you add additional criteria. Type the 4 character codes into the search box(es) and you’re set. I’ve forgotten the actual codes and offloaded my old files to DVDs a year ago. But if you can find one such file, just dragging it into the search box will display the actual code!
Find then gives an active Finder style listing of all the matches. You can tag or open files from that list, singly or in batches, including via control-clicks. Very slick. Oddly it can’t search for Finder tags, at least not beyond the default color labels. But the Finder can search for them and its searches can be saved as smart folders.