The small amount of oil left in the filter between changes is negligible in practice.. In my case it results in about 5.4qts being installed instead of 6. So about 10% is used oil. I hesitate to call it dirty or old as it is neither, just the additives in the oil have been consumed and need to be replenished. If anybody has followed long OCI UOAs, you will have seen the effect that even a quart of make up oil can have on TBN, often raising it several points higher than you would think for the volume added.
Optimally I wouldve liked to have done UOAs on every oil change I had done, but it recent times it has been hard to do anything during normal person (daylight) hours including shipping things out so it was just too much hassle. I still have the last two UOA bottles I filled from other vehicles sitting in the garage
somewhere. One is over a year old and the other is probably 2 years at this point.
Anyway, my reasoning is if its not plugged then it is still filtering and if its still filtering then why change it. Its more mess than is necessary. Modern vehicles don't make that much trash anyways. IIRC, most of the stuff a oil filter picks up is stuff that the air filter missed, and, I have that end covered with a Amsoil EAA and a restriction gauge to monitor filter plugging.
Honestly, I kinda had to roll my eyes when I saw this thread. We have one of these, what, twice a month? Usually with the same title, too, just different authors. They always end up the same way with the same people on both sides posting their opinions and no one ever changes their mind so its kinda like watching a rerun of an old movie. I haven't been in on one for probably a year, so, I thought I would watch this rerun.
