Before I retired I worked in a contract research laboratory that tested pesticides for the EPA and pharmaceuticals for the FDA. The tests were paid for by the company that made the materials and the results of the tests sent to the appropriate government agency.
The test for the expiration date is called a storage stability test. It involves storing the material at a constant temperature and periodically removing a sample and testing it for chemical purity. If the purity drops below a given level within a year, the expiration date is assigned appropriately. If no appreciable loss in purity occurs within a year, the experiment is halted and the material is given an expiration date of one year. The one year time span is usually chosen because all these tests are expensive and the companies don't want to spend more than necessary. In addition, it is possible that extending the study may delay the release of the product and that would be really expensive.
The takehome message is to place close attention to the expiration date for a drug with an expiration date that is less than one year - that is likely to be important. If the expiration date is one year, the drug MAY be stable for much longer than that but there is no guarantee.
My wife is also a retired Pharmacy Technician and keeps a close watch on our OTC meds, both for use in the home and in the coach. She has thrown out many bottles of pills that are out of date.
If any of you use a checklist, "Check expiration dates on meds" might be an item to include.
Then your wife should know that those dates on OTC drugs are for the most part arbitrary, and that most OTC meds are good way past the expiration date. Here's an article from Harvard medical school (just one of many articles on this subject from highly reputable sources):
Guess you missed the following line in that story: "Placing a medication in a cool place, such as a refrigerator, will help a drug remain potent for many years." You aren't going to find those kind of conditions in most RV storage cabinets! Our meds, both otc and scripts are kept in a Go Bag at home and moved to the motorhome when traveling. Grab and run if needed.