At least i have not own the 309 long enough to witness such a change.
As for the availability of brushed or polished Ti, if i am not mistaken, while there is no completely polished Ti Lumes, there is a few or one that has a combi of brushed and polished Ti, polished being on the bezel.
But i'm not that much of a luminor guy, so the others would have to help you in this!
Cheers
Stephen
has somewhat the "healing" effect ...
no polished, all are produced with the brushed finish
Titanium (slowly) forms an oxide coating in contact with air, which will dull any efforts at polishing, and also accounts for colour changes as the oxide layer thickens.