I have been loading some 1969 headstamped 7.62 Lake City cases that had bullets pulled. I resized them and have been loading them with no problems. These were unfired cases.
I could be wrong but i believe the only thing that will harden the brass is work hardening. What i mean by work hardening is when you fire and size brass. in my opinion, brass casings cannot work harden by sitting around for years. Someone else with more experience may chime in.
Any ammonia in the air (think cat litter box, house cleaning supplies, etc.) can slowly harden brass over the years, so storage conditions can play a factor. I've loaded a lot of old brass and never had a problem personally, but I have heard of a few instances of people having problems like case neck cracking during bullet seating or on first firing. The cause was eventually traced back to poor storage.
Keep in mind that annealing again shouldn't hurt the brass.
Annealing comes in stages, once it reaches 'Optimum' you have to overheat it to ruin it.
If you aren't overheating the brass when you anneal, you can run it through again with no ill effects.
Annealing is 'Optimum' when the brass comes out of the dies with no variation you can detect.
I'd size a few and see if you can find variation, if not, they are ready to load.
I ran some thru the neck sizer with an expander ball. Then miked the necks as I rotated the case, has .001 OD variation which I attribute to simply being factory RP brass, from .304-.305". I can live with that. Thanks to all who responded.
It will be a question of how they survive over time.
I got a barrel full of .30 US (military version of .30-06) made during, or just after WWII.
I was feeding them to an M1 Garand, so not exactly a .30-06 but pretty close in loading.
Some didn't get annealed, and some did.
The annealed versions lasted a little longer, while the 'Vintage' brass only lasted 2 or 3 reloads before cracking.
I attribute this to the grade of the brass, war time brass was quite low in zinc, and often used tin in the alloy,
Tin doesn't stretch well, all the brass was pretty well done when I started finding stretched side walls, getting ready to head separate.
I've found this to be true with pretty much all WWII and Korean war brass made in the US.
30 years ago, zinc was a little lower, but tin had been removed entirely in most US civilian brass (tin used to be a war time 'Filler' when copper & zinc was in short supply).
12 years ago brass alloy was almost exactly what it is today, depending on manufacturer.
Since you are firing civilian brass that probably has zero tin and proper amount of zinc, I'm sure you'll do fine.