Thanks, as always, Alan ... for your enlightening explanation. Another ...... ? possibility I'd been "chewing" over - (
... there I go again !) - is based on a long-held theory [of MINE ] that supermarket chains MIGHT, from time to time, be given "first refusal" as it were, on batches of sub-standard and/or inferior goods (that manufacturers would otherwise find difficult to dispose of through the normal channels) and thereby, in turn, pass them on in bulk sale to unsuspecting consumers.