Walter, when I first bought Last preservative for lp records (as vinyl was known in those days), the information declared it good for 200 plays or 10 years. I notice there is now no mention on your site of any time limit the preservative should last on the record. Have you found that it lasts the life of the record?
We do know the following: If is record is kept well cleaned prior to play, a single treatment is good for a minimum of 400 plays with out measurable wear. Most records can exceed that by substantial margins. We have test records with an excess of mare than 1000 plays without wear.
However, the limit for each music lover is unknown and probably unknowable. What is the condition of the playback stylus? What about the stylus suspension system? What is the precision of the cartridge/stylus/tone arm/turntable setup and alignment? Any (and all) can have an effect on record wear, or lack thereof. A substantial unknown is the quality of the original vinyl. That can range from some of the Japanese Super Vinyls, to the K-Tel records which were made with recycled vinyl (including ground up labels).
What we are able to say with assurance is, if a record has received 200 clean plays – it can be retreated and is good for another 200.
I hope this is helpful,