You're still missing my point mate. Retrospective red cards have been issued for years but only when the ref has missed (or claimed to have missed) an incident and the player wasn't carded at the time. Aguero, Balotelli and Adebayor all spring to mind.
The Thatcher incident was, as far as I'm aware, the only case where a yellow card was issued during the game but was retrospectively changed to a red by the PL/FA a couple of days later. Horrible though the incident was and deserving of a red card, the PL/FA broke their own rule of not retrospectively changing a yellow to a red because they always said in such a case the referee had seen the incident and dealt with it on the field (with a yellow card).