Obviously, you need one signed form from each model, but otherwise it depends on the wording of the release; you could have one that covers multiple shoots. Just make sure that this fact is communicated clearly.

In theory, a model could claim they just signed something at the first shoot which they were told is "the standard model release" and that they were deceived about it covering multiple shoots because that was hidden in the small print. In theory, they could try to sue you on those grounds.

Having one form signed per shoot is the most certain method to ensure you'd win that case, but if you have the dates of the individual shoots (or a date range) listed prominently on the form and have witnesses that you mentioned this explicitly to the models, then you're pretty safe as well.