There are many thoughts of oil breakdown. If it does breakdown in short period of time, (3 to 7.5k or 6 months) then why are trucks, like my friends, who changes oil filter every 10k, only caps what is needed to maintain full lube level, sends in a sample for analysis, and has over 80k on the original oil fill, results still within oil specs so far and more miles to come. I'm at the beginning of a long term run myself.
In the 60's and 70's they use to collect and reprocess spent oil. The problem was the cleaning out the additives, collecting the clean oil itself and reprocessing for sale. Test taken then proved it was identical to unused oil sold. Legal was active then as today, and said if it went through the engine once, it could only be sold as reclaimed oil no matter what test results indicated. Cost factor per gallon was to high and they stopped the process.