As many of you know, the warp drive scale was recalculated at some point between TOS and TNG so that warp 10 is now infinite velocity. In other words, starships can't exceed warp 10 like the Enterprise does in That Which Survives.
In The Search for Spock the new Excelsior class ship is said to have "trans-warp" drive which is significantly faster than the old warp drives of the Enterprise. Is it possible that the new trans-warp technology became the standard and was eventually called simply warp drive? And as a result the Federation changed how they define warp speeds? Any evidence in universe or out of universe point either way?
Of course, this assumes that the E-D passing warp 10 in season 1 TNG was an error of some kind.