Still resolving this, very slowly. Find and Replace cannot help because it does not have option to change field I now know I need to change. The problems moving music to new HDD and retaining JRiver library have been manifold, so sharing below in case anyone else ever has misfortune of same peculiar circumstances, or just to note a practice to avoid (numeric characters in volume name).
• All, or most, single-audio-album-files split by cue sheets failed / were not properly retained when I used Replace, Move, Copy to route library to new HDD; all that was left was a single file, no splitting. I have seen this before, and other users noted in past— might not be issue for someone starting a new library now and moving later. Dunno. Seems likely though. Anyhow, I got past this by restoring library, then manually editing, in TextEdit, the "field (filename).jmd" file in the JRiver library folder.
• However, I then saw, though everything was happily in place (each file, from cue or not, in any playlist where it had been, and retaining play counts, etc…) that once an auto import was completed, a whole bunch of tracks went missing from any playlist they were in, and had play counts reset, and ended up in "Recently Imported" smartlist like they were new. Not just files from cue sheets… any files. Any files that were… track number 10! So, I then realized, snooping around the field (filename).jmd file in the JRiver library folder and other settings files, that …
• Because my old external hard drive's name started with the number 10, JRiver all along has been seeing Volumes/10restofHDDname and erroneously creating extra directories for any track number 10, making false paths in the library, and now that I was migrating library to point to to new HDD, with different name, all track number 10 files (any format) were vanishing and being reimported, lost from playlist, and sometimes replaced by track number 1 from same album. What a mess.
• So, I restore again. I changed main new path again in the field (filename).jmd file in the JRiver library folder, as well as in images jmd file, etc, and went through and got rid of all the extra paths made for all track 10s. This fixed all the non-cue sheet related files. Along the way, false volume showing 10 at start of (new!) HDD name now showed up in the Files interface. I meticulously deleted dupes not in there, which is where the original files temporarily resided, and like other steps had to do this with actual files / HDD not mounted so as to not initiate auto import. but…
• once an auto import was completed, all track number 10 songs from cue sheet associated albums were vanishing as before. So, I restored to most recent previous point and saw this is because all the cue-sheet-associated track number 10 songs were missing the semicolon and number at end, as in
FileName.extension;10
they were supposed to have, as seen when viewed as Filename (name) because unlike
FileName.extension;1
thru
FileName.extension;11
etc
since JRiver had made false paths all along, all the track 10 songs from split cue files were wrongly seen as the one and only file associated with cue sheet, and therefore Filename (name) read as simply
FileName.extension
for all track 10 songs, and so upon autoimport, those would vanish, a properly named ";10" Filename (name) would appear, but would not know to go into playlists, retain play counts, or any other existing settings.
So then…
• I needed to see all my track 10 songs from split cue sheets.
No smart playlist option for that, so I finally realized a smart playlist showing all track 10s with stipulation
Playback Range » is not <empty>
would show those, since split cue sheets rely on Playback Range for track durations.
However, as noted above, Find and Replace cannot help because Filename (name) unfortunately is not a field it can change.
So now I am manually going thru all those files (only ones in a playlist, or with play count ≠ zero — because I don't care if others get reimported as if new) as viewed in smart playlist and adding
;10
to end of Filename (name)
of each
So, I would say—— don't ever start (or end?) name of the HDD with numeric characters, if that's where you're housing your JRiver music.