Vintage sub experts: once and for all - bezel direction

[thejerseyrock]

Vintage submariner experts: forgive me if this has been asked and answered before, but… I've searched on TRF and on the Google, and while I've found answers, none have been definitive (conflicting responses) or well-explained (source of information / proof of answer)

on these submariners:

A) 1970 Mark IV 1680 red

B) 1968 5513 meters first

should the bezels be unidirectional (counter-clockwise for a dive watch) or bidirectional…

or, does... "it depend" ...and if so, why? (for example, bi-directional, but you can/could lock them in place, etc etc)

If they used to be bi-directional, when did it change?

thank you