> Franklin was pretty clear on the helical structure

the type of diffraction her lab was doing only makes sense on helical structures. it being helical was already kind of? established -- linus pauling was contemporaneously working on some sort of alpha-helix inspired single helix model.

watson and crick immediately recognized the position of the diffraction spots fit the distances suggested by their chemical modeling of a, t, c, g, which franklin was not able to do since she hadn't made a structural prediction.

> postulated ahead based on partial data

not quite. if you know that a t c and g are the raw chemicals made, you can make a (possibly even literal) model and say, "this ball and stick model predicts diffractions here".

this is arguably better science than waiting for data and fitting a model to the data, falsifiability and all that.