I never used the Append function in the 1990s. I just kept in mind that I needed to record a couple of seconds of silence after the last song (I think my recorder had a REC MUTE button that you could push during the recording to record 4 seconds of digital silence and then stop). Then I would rewind the tape a little, play it back to the end of the last track and stop the playback while the muted tape was playing. Then I would put it on Rec Pause.
The recorder will continue the time codes recorded on tape if you start the recording in the middle of an existing recording. If there is an interruption of the absolute time code recording, the tape becomes a User Tape instead of a Super User Tape and you can’t renumber it.