That's a shame however if they are only meant to be changed weekly it's no big loss, unless like my friend did you get them on a generic prescription with enough to change regularly.
I think that was probably a fluke and at some point someone would have noticed and tried to ration her to one a week.
The likelihood of a plaster still being in place after a week on someone active who showers daily is closed to zero, and if it is still hanging on, the probability of it still delivering anything meaningful across the skin is even lower.