The first chicks I got from Privett, by way of a feed store up in Denver, were Wyandottes. I got them five and a half years ago, and they're still laying.
Since then, I have EEs, that are still laying after four years, but soft shelled eggs are now a problem. One EE died not long ago of crop problems, but she hadn't laid in a year.
I have three-year old Sussex that are still laying, and no problems.
The most recent are Welsummers, a year old, and they have all been great layers so far. There was a problem with that batch of chicks, though. It had been in the news that Privett had been cited by the health department for salmonella contamination. This was after I had just gotten the chicks from them. I went so far as to collect flock stool samples and sent them off for testing. The tests were all negative for all pathogens.
I've heard Privett has had all sorts of problems, and I would rather not use them in the future, but all the feed stores around here use them. I've heard raves about My Pet Chicken and may give them a try.
For all your breeds to have such a short laying career seems odd. I would examine environmental causes since this has affected almost all of them. Something in your soil perhaps? Are you down wind of any commercial farming? Noise levels? Is your neighborhood adjacent to loud manufacturing operations, gravel and cement producers? High noise levels can affect laying.
But it's entirely possible Privett has let their breeding stock quality diminish and their chicks just aren't up to par. Like I say, I'd rather not continue using them.