I found out that some things I had bought cheaply were originally supplied in bulk for secondary manufacturers from even bigger factories. With things like adhesives, sealants, and herbicides the expiration date for bulk supplies is stamped on the crate supplied to the secondary manufacturer but not necessarily on the individual tube or package.
For certain products the shelf life might be three years, whereupon the product might be only 80% effective and cannot be used by the secondary manufacturer. They sell the soon-to-expire bulk crates on, often at a massively discounted rate rather than pay disposal fees.
There are some “businesses” that specifically target remaindered stock. They pay close to nothing for it and break up the bulk crates and sell them on to individual consumers. A decent proportion of the time it won’t matter in terms of performance but if you get what you think is a reputable product cheaply and it doesn’t perform then this can sometimes be because it’s sat in a warehouse somewhere for years.
