Hey Jen, good question.
If you were to compare a tip and overlay versus a sculpted enhancement in strength - chances are the sculptured would win. Why? Because the tip is a much weaker polymer designed to simply give you a surface to apply to.
Saying that - during repairs and full sets where forms are used for extending the length of the nail, many times, techs accidentally get seepage under the nail which can easily catch and 'snap' that sculpted area off.
Chances are... this was the case with your situation.
Product adheres perfectly well to existing product so there are no 'seams' of weak areas (unless your finishing is really really bad - but thats an entirely different cup o fish
Hope this helps!