As far as I can tell, there was no "maximising models in btb on the charge rule" in 3rd edition. However, there was a specified maximum wheeling angle: 22,5 degrees, and there was no free wheel to close the door. Indeed, movement was not determined by unit, but by model. So, some models might be able to end up in full btb this turn, and others might not, in which case the latter would not be in cc that turn, and the unit's formation would count as "disrupted/unformed."
Hence, there is no clear answer to the question, as it would depend on individual circumstances.