if your talking about the PET bottles I had 2 dozen of them but chuckled them after a few brews in them .I don't know about oxidation but they were a prick to clean properly . I was always trying to get crap out of the little feet .
PET is soft and easily scratched. That "crap" you saw in the bottom of the feet was probably scratches on the
outside of the bottom of the bottle. A lot of people have fallen for that trick.
I've been using some Coopers PET bottles for years. Even leave them for a week with cap on when empty before cleaning them (never use anything abrasive to clean them - no bottle brush).
Coopers themselves have stated that their PET bottles are good to hold beer for up to 18 months. This is fine for most beer which should be drunk fresh as soon as it has conditioned. Some people like to age stouts and other richer more complex beers for longer. This should go in glass.
Beware of other brands of brown PET bottles. Coopers bottles are better made.
As for producing off flavors, I call BS. Some home brew competitions now require entries to be submitted in PET (to avoid the risk of glass bottle bombs). No reports from judges as far as I know of entries being contaminated by plastic flavors.
What people say they taste is often driven by confirmation bias. Say to some people "Taste this. Do you think it tastes like plastic?", and they will say they taste plastic.
Plastic has had a bad press, and haters and going to hate.
