Mine is 20, and it's less of an issue than I previously thought. I contacted Surly and got a speedy reply which stated among other things that they were not aware of and disc clearance issues but wanted as much info as possible in order to resolve it for me asap. nice guys! Also, there is some question about whether there is any QC issue at all (check the threads here). At any rate, I wouldn't think given the info we have that the QC issue (if there is one) is related to this at all.
By the way, I installed my old avid with a newer mount last night and went for a ride with no problems. but the clearance is literally paper thin, so I'm definitely going to need to get it faced soon (which is a good idea anyway I guess).