These have both been selling for a couple of years-ish now. The Cox and others from the same sheet have been known for many years, actually. They are print flaws, not variations, which were created by the red ink orientation for a different sheet being applied to the back. This only affects the managers and the players who are in the spots meant for managers (Oscar Azocar is an example). But they were not design changes or corrected mistakes.
The 1990 Topps Checklist is fairly tough to acquire and is a rare instance of a very newly discovered true variation where Topps made a plate change to corrected a mistake.