Are you sure what you're seeing isn't paper? I've come across a handful of records over the years exactly like what you're describing that have "contaminated" vinyl with bits of cardboard and paper in the vinyl.
I can only assume that they were pressed during the oil-embargo 70's era when so many plants were recycling vinyl and labels, etc. got in the mix.
I can only assume that they were pressed during the oil-embargo 70's era when so many plants were recycling vinyl and labels, etc. got in the mix.