I have re-sized R-P brass that was bought new (by me) about 20 years ago - 7x57 - I loaded and fired them then, maybe once or twice - perhaps 1 out of 20 would split neck, when I just tried to re-size them - not sure I had seen any split necks previous to that. I am told that proper annealing will soften it up and the splits will stop. But assumes that all case makers at all times and in all countries, used the exact same alloy of "brass" and same processing of it - which they did not and do not - is most definitely a thing about "corrosion" occurring over decades - some might use less technical term of "age hardening" - but might be specific to the alloy used when that case was made, and what it has experienced since it was made. Generally, I would not consider cases that are 10 years old to be "old", and would not expect them to be much different today, than when they were made. But I could be incorrect about that.
I recently processed circa 250 W-W brass that had been delivered in cardboard box - unknown ages - factory ammo that had been fired - still had what I believe to be the factory primers in them - the shooter had been "keeping" his brass, but never did get into re-loading - 22-250 cases. I found four split necks out of that 250 or so fired brass - not sure shooter even noticed that, or if the splits occurred sometime after the round had been fired. There were lesser amounts of other head stamps - I only picked out the W-W stuff - others have had nothing done to them - headstamps by Barnes, R-P, etc.
In this day and age, no assurance at all that the head stamp has much to do with who made it - classic is the various "Weatherby" headstamped brass here - I am told that Weatherby never made brass cases - were made by Norma, originally - I have no clue who makes them now. So I presume that W-W, R-P, Barnes, Ruag, etc. could now be made about anywhere by who knows who - but might have head stamp of what brand they were sold as. Specifically, is a few bags of Ruag, USA brand brass here - at least that is what label on bag says - each case is head stamped as "MFS" - which is a case maker in Hungary, I think - so I presume is other cases made by same "MFS", with some body else's label on the bag.