Where on your cases were the splits. I have some Kynoch 404 Jeffery ammo dated around the early 60's and about 1 or 2 in every 5 rounds I fire suffer small splits in the case neck. I regularly anneal the neck and shoulders of cases that do not split when first fired and these don't give any further problems. I silver solder the neck splits on the defect cases and with regular annealing I haven't lost any of these repaired cases either.

I think the issue with Kynoch split cases is one of age, and possible poor annealing. Brass does harden with age, annealing fixes it.