Hey there!
My TI flats sport the same marks you describe. In fact, all the flats that I've used (from other brands) ended up showing these same marks if left long enough.
It's like small indentations where the strings contact the frets, right?
In my experience this has never been a problem at all: I don't feel it while playing and I haven't noticed any worsening in the string functions (tuning/intonation issues), so I don't see any reason for a string change.
If you're worried about that leading to string break, what I can tell you is that every time I've broken a flatwound it was always at the silk part (where you wrap it around the tuning pegs). And that was caused by excessive string switching, rather than by simple use (string sets that I switched the most had the silk wrap zone weakened).