I have had this happen with Roto 77s and my guess is that it could happen with other flats
I have a 4 years old set of Chromes, heavily used (they were for two years on the only bass I had those days), still sounding great and with any intnation or tuning problems.
3 years old Thomastik, switched lots of times from bass to bass, or just to try other strings, and they sound like this today: https://www.dropbox.com/s/4md9hmtw73u458o/P50 Thomastik.zip
these samples are from three days ago, switched to the Classic 50's Pbass from my assembled P (their "main" bass).
Rotos are probably the only flats with an actual short life-span... I've tried them years ago, and they lasted me for a month or less more.