Having spent a working lifetime in and around the gardening supply trade, so far as I know, the same procedure occurs.
Your ‘garden centre/retailer’ receives on sale or return terms ,from the seed supplier in Jan/feb, a display rack complete with the packet-ed seed selection. Sales are made into the season, with top-ups requested at intervals. Around the end of July, the seeds are withdrawn and returned to supplier for credit.You may have noticed this if you go to buy autumn sowed varieties- they have none!
The seed supplier then re-cycles the stock, adding some fresh seed to improve the overall germination figure*, repackages and gets them back into the sellers just after Christmas .
*This used to be specified for vegetables under The SeedsAct1920, currently I dont know.Obviously, there is scope for not mixing, not sampling etc. Another question not answered is what is done with the “late returns”
Some non specialist majors crash -out their remaining stock cheaply, having bought outright.
