yeah sounds like your ripping into the chrome. if you damage this plastic with stripper or thinners or any harsh solvent you will ruin them.
When the chrome is stripped off them they look like this...green or cream ABS type plastic.
This one had a lot of paint and primer over the flaking chrome, you can see here where its melted the plastic. once this is damaged, you loose the grain/pattern in the plastic. you need this intact to get the candy effect when repainting.
The chrome and condition of the tail lights can look fine, but the chrome is a shell around 40 year old plastic thats deteriorated and decaying. you can see pitting here in the plastic. i find this most with plastic parts on the outside of the car, that have been exposed to the sun, and exhaust fumes, where as interior parts like dash vents and console surrounds are better, because they have had less exposure.
The plastic then has to be rubbed with 800, then 1500 grade wet and dry sandpaper. Then copper coated. you can see here that the copper dosnt fill in much at all, some times i get it coppered twice and the pitting still shows.
The copper is rubbed now with 2000 grade wet and dry before nickel and chrome
this tail light had a small chunk taken out of the rim...i got it plastic welded to fill it in, but air bubbles in the plastic still showed after i filed and sanded it back. we coppered these three times, and you can still see little pits in the plastic.