Vredstein winter tyres have cracked!

[MPETT]

I've have 235/35/19 Vredstein wintrac extreme tyres fitted to e46 m3 alloys (4xfronts) and they have worked a treat in 2 winters gone by. I put them in storage again and brought them back out this December. I had the alloys refurbed and got the tyres refitted. When I went to pick them up 2 of the tyres had failed on the shoulder of the tyre. The first tyre had a number of cracks in the rubber they were all in the same direction and ran parallel to each other. 2 small egg shapes were pushing through 2 of the cracks!.

The second failure wasn't apparent until the car was driven. A horrible vibration came from one of the wheels and when removed on the inside of the shoulder of the tyre was a crack around about 60degrees of the circumference.
Am I just unlucky, has the tyre rubber gone hard over time, has the rubber been damaged by being stored in a barn (heat in the summer) or have I used a st tyre fitting company that have pinched the tyres when they fitted the tyres to the refurbed alloys?. Advice welcome. I got a second hand replacement but need another one. Thinking the winter is almost over so should be thinking about summer tyres!

[TooMany2cvs]

What's the manufacture date on 'em? (Four digit number, in a small oval, just after the letters DOT on one sidewall - WWYY)

But that looks like damage to me.