From my experience in ammunition procurement in LE, manufacturers change specs, packaging and components frequently, without notification or warning. Primers, propellant, cases, pressure levels, even details of the actual projectile can vary from lot to lot, year to year. Some of it marketing driven - what they think people will buy - and some of it is driven on component availability and consistency. Sometimes it is due to differences in measuring equipment and firearms used. And they rarely announce changes, even when it impacts reliability and performance.
One well-known manufacturer changed primers and it caused misfires. Another well-known manufacturer didn't adequately control it's bullet manufacturing process, and the contract-winning projectile that did great in testing suddenly stopped expanding altogether. A third well-known manufacturer changed the velocity specs and the load no longer shot to point of aim. All without warning or notice. I could go on for an entire book.
After decades of nonsense like this, my agency specified that ANY change to the components or performance specs required notification and retesting before acceptance. But we bought tens of millions of rounds of ammo, and had the reputational position to demand that. John Q Shooter does not.
If you don't have access to a chronograph and testing media, you are relying solely on the manufacturers claims, which sometimes leave much to be desired. I prefer to "trust, but verify". When you find a lot of particular ammunition that meets your needs, BUY LOTS OF IT. It will rarely be the same thing the next time you find it.
