Since this is about using flats over many years I thought resurrecting an older thread would be appropriate.
Just had a conversation on this subject with my bass tech (Winchester, MA) as I have the La Bella Jamerson set on my P bass going on 8 years. He was telling me that as strings get older they tend to lose their consistency even if you set the intonation at the 12th fret they may not be consistent over the full length of the string. I notice that my strings have minimal tone (although I like the "thud") and their playability is beginning to resemble rubber bands. I used a strobe tuner to verify his observations and I believe that for this particular set it is time to restring. The only down side is that I will have to break in a new flatwound set and that usually takes the better part of a year, but I just learned a lesson and thought why not share with other TBers since I have learned alot from many of your posts (although I do have a very large ignore list

).