Here, they pay for the days reserved for them, regardless of attendance.

It was only recently I'd even heard about banked days - like you, it was a local provider who had been asked by a parent and was wondering if it was common place.

Here, it doesn't seem to be. Afterall, can you imagine if grandparents came here for Christmas for three weeks and wanted to see/look after the grandchildren, and we had to bank/provide credit for those days. Heck no.