https://kottke.org/26/03/0048598-a-generator-for-vhs-slipc
A generator for VHS slipcovers, cassette tape inserts, CD la...
cassette tapegeneratorvhsslipcoversinserts
https://www.nationalaudiocompany.com/faq/why-are-cassette-case-inserts-named-with-letters/
Why Are Cassette Case Inserts Named With Letters? - National Audio Company
The letter refers to the shape seen when you view the edge of the insert. Its folded shape looks like a J, an O, or a U. J-Cards and U-Cards may include extra
case insertscassette