Tolerances are always an issue. I have an older Dr. Rocket 38/480 case that about 1 in 10 phenolic liners won't fit in without a lot of sanding.
I bought an Aerotech case and the liners that don't fit the Dr. Rocket case will slide right in the Aerotech case. I think I got lucky with the new case. Both were built to the same specs, but obviously the tolerances were on other end. BTW, I had to peel the label off the Aerotech case because it wouldn't fit in a 38mm MMT. Tolerances again.
I'm sure the tolerances on paper liners are way bigger and farther off than phenolic. Peeling a layer is much easier than sanding phenolic.