Good analysis Steve. The intentional change definition sounds simple but can be complicated in practice. It Topps adds a option or traded line that is easy, but it is often impossible to tell if a defect was discovered and intentionally changed or not
Another good example are DPs. In the last printed Standard Catalog Lemke listed variations for the 52 Mantle, Thompson and Robinson. PSA does not recognize them. The differences can be found on the front and back. The differences were likely not intended but did result from an intentional decision to DP those 3 cards
George Vrecheck has written articles on DP differences in the 63 and 55 (56?) sets. Green tint non pose differences from 62 are another example. Probably not intended but did result from an intentional change in the printing process. Variations ?
Bet a lot of 52 Master collectors are praying PSA does not adopt the 52 Mantle as a variation
It would be tough to come up with a hobby definition that all would buy into or that would cover all past and future official variations