You're refining and recycling ideas. everyone does it. Elvis Costello is one of the most prolific and fabulous songwriters I know and he started to do just that from about 1990...snippets of melody, themes, arrangements but each time it went somewhere a little different. he only lost the plot with his last marriage - moving into areas that stretched him too far and that brought on some wholesale reruns of melodies and even songs that he'd left behind were taken up and recorded. Even then the amount of new invention made some of those his better songs in a decade.
IF you think you're replaying yourself then make a key change or move that idea to the counter melody line and write something to go over it.
MOST OF ALL...it's normal...it's easier for us to put work out to be heard so, sometimes, we "publish" what we would have put back in the folder for revisiting.


Cheers
rayc
"What's so funny about peace, love & understanding?" - N.Lowe