The first one will work in your MK20. That sloped shoulder on the outbound side of the threads is, I believe what they removed with the universal retainer in the MK20 recall. I think that shoulder, when torqued excessively, was putting some pressure on the MK20 body and that's what caused the few spectacular splits. Anyhow, the newer retainer has a flat shoulder.
Measure the length of the 2nd retainer, I bet it's a few mm longer than the first. If so, it's for a MK5. Those are hard to find and someone might pay some real money for it.
I've heard that there are DIN retainers for older MK2 and maybe MK200 that look like that one, but I'm not familiar with them. Maybe DA aquamaster would know more about it, he usually does!