BCNF: superkey or candidate key ?

C.J. Date in a recent text defines BCNF in terms of superkey. ... every nontrivial FD A -> B satisfied by R, A is a superkey for R.

Previously he (and others) defined it where A had to be a candidate key (which is irreducible).

The two are not equivalent. The prior definition was more strict. What is the accepted definition du jour ? And what motivated the change ?

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