Wetherby brass is packaged in cardboard boxes, and as stated ive had new but older unfired brass develop splits while sitting.
Over the last 5 years or so ive also (inherited) several hundred rounds of modified Wetherby 378 brass and also several hundred of 300.
Some had only been fire formed and sorted for weight, and all were in the original boxes. It really wasent worth my time to sort thru it all, at least 90% got chucked for various reasons. I also received 3 full boxes of 20 each new unfired 300 wby necked down to 6.5 and I ended up chucking all of them after resizing up to 7mm. I did not anneal them before doing so, and splits developed after they sat for awhile. With large capacity modified cases its best to use new or once fired brass for hunting long range, after that use it for practice.