The result of this is often, especially in the case of some players who habitually play on the very edge of legality, that some moves in a game are later found to have been technically illegal (the current record is 34 by Vic Stannard.) However, no penalty is EVER applied to a player who has "got away with it" by playing an illegal move that was not buzzed: if the other player(s) in a game accept the move, it is considered to have been as legal as, for instance, bluffing your opponent into conceding in a game of poker when his hand was better than yours. (This attitude almost certainly springs from the long history of MC in gambling casinos.)
In fact, quite often, a player will accept a move as "legal" even when he knows perfectly well that, if he were to buzz it, it would be declared illegal: this is invariably because he is sufficiently impressed with the bluff to wish to adopt it himself for future games, quite possibly in the return match against the same player (because it is Such Incredibly Bad Manners to buzz somebody for committing the same illegality you played against them in the previous game). In doing this, a Precedent is set, and other players may quote this Precedent in subsequent matches: and if enough other players do so over a sufficient period of time, then the IMCS's policy is to write a special-case clause for the manoeuvre in question, making it legal. It is certain that the Engelbert Manoeuvre became legal in exactly this way: and highly likely that the Ongar Denial also did so.