Expiration dates versus codes I can't read?

Many edible grocery store items have expiration dates printed on their containers. I like that—especially the ones that go the extra mile and read, “Discard X-days after opening.”
Why do some products have codes instead of dates? I’m sure the codes are very helpful to the manufacturers, and that they allow them access to pertinent information including—but not limited to—the date of manufacture, the lot, etc.
But why can’t they simply add an expiration date?
Also, is there a web site that will allow me to enter the codes and thereby discover, if not the expiration date, then the date of manufacture from which I can add the appropriate amount of time to glean the expiration date for myself? “When in doubt, [I do] throw it out,” and I throw out a lot of items I might be able to keep if there was simply an easy way to verify when the point of safety has passed.

Some manufacturers use codes instead of ‘open dating’ because shoppers tend to go thru the shelf, looking for the newest ones. Thus more likely to have some left on the shelf until they are outdated, when the store returns them for credit. So many manufacturers believe that open dating results in higher returns, and thus higher costs to them. (Also, the excess handling by shoppers when picking thru the items tends to leave the display disarranged, thus reducing sales.)

Generally, if the manufacturer is using codes, it’s because they do NOT want the manufacturing dates known. So there is usually not website or similar easy way to find out the corresponding dates. You can call the manufacturer and ask, sometimes they will tell you for your one item.