I think they use the dates for inventory control. There is no law that says they must sell by the BB date - look at all the "scratch and dent" discount grocery store that sell out of date items. The exception is baby food which can not be sold when expired.
In the food shelf where I volunteer we accept donations up to one year "past". (except for baby food). Older than that, gets given to a pig farmer. (Donors are not told that though). We get some really old donations, even from the bins in the supermarket, which means people are bringing their old food from home for the donation bins.
Once in a while we get a donation we refer to as "Grandma went into the nursing home", as you can tell they cleaned out the cupboards of everything, old, new, opened, unopened and gave it all to us. Oh well, I guess it is the thought that counts. Oldest one I ever saw was a package of Jello pudding from 1969.
I do notice that newer products are coming through with a later date. It used to be like one year past the manufacture date, now we are seeing BB dates into 2022.