At least, that is the way it is supposed to work.
I contacted Harman Technology support in October 2022 with the following question:
"Your website says my unopened Ilford Rapid Fixer should be good for "two years," and my Simplicity Ilfosol 3 sachets should be good for "18 months." But from when does that time start? I can't find any manufacturing dates or expiration dates on your products."
After I furnished Harman with the batch numbers from their packaging, it was determined that the Simplicity Ilfosol 3 had a manufacturing date of Nov 2018, so should have been good until May 2020 -- but when I bought it from B&H in Feb 2022, it was already 21 months older than its use-by-date.
Harman tech support was very helpful -- they replaced the developer at no cost to me and they gave me a couple of bottles of fixer as well, even though those were in-date when I bought them. And she said they would follow up with B&H about their inventory management.
BTW, the last Kodak brand chemistry I purchased was a bag of D-76 I got from B&H in Sept of 2024, and it is stamped with an actual Expiration date, which I much prefer to Harman's indecipherable "batch numbers."