All the "frozen" ATP means you've taken the writtens. A long time ago you had to have 1500 hours to even take the written test for the FAA ATP. Had to take your log book to the FSDO/GADO and get a form saying you could take the written. They quite doing that years ago. The CAA world would let you do the writtens (all 15 or whatever) anytime. I've seen some comments that you could use their ATP writtens for their COM and not have to redo the tests but I don't know that for sure.

So there are plenty of pilots with "Frozen ATPs" in the US, they just don't know it.