I doubt the answers you received from you Q&A is the same for all LEGOs store. I've talked extensively to the Store Managers about PAB at the 2 local LEGO store by me and I've received answers.
How often do the PAB bins change over?
Sometimes the store will receive new elements within from time to time, but overall, the inventory stays the same. As posted in the store calendar for January, you'll start to see a significant change in inventory.
Do you control what goes in the bin?
I know this is true because this answer was asked at the Bricks by the Bay LEGO convention last year and was answered by Steve Witt. Stores do not and cannot request PAB elements. They just get what's sent to them and usually it's the same across all stores. The elements sent to stores is overstock from the warehouse.
Do you still do birthday parties in the store?
My local LEGO stores still do them and they don't do it while the store opens, it's done before the store opens.
As far as PAB elements being swept up from the floor and then thrown away? My stores do sweep them up, but they get cleaned in the back and then sorted into bulk PAB grab bags for $7.99 each.
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