That is incorrect, see here how it really works:
We are discussing different things...
-) at still film cameras for praktical reason (easy access and easy change between printing and non printing version) a exposure from the back was introduced and stuck to.
-) at
cine cameras (and only very few models offer such anyway) exposure takes place from the front.
"Time-stamp" is the film printing version of time-coding in cinematography.
Film manufacturers already offer a signing by which a length and frame information (eye- and machine-readable) is printed onto the raw stock, which is benefitial at editing.
More versatile though is a system at which at taking a coding is done: Time-Coding.
This coding can be applied to a data-file, to a video-tape or to cine-film. And the latter is what we are talking about. There are basically two systems applied for this time-stamp.