I saw that Davidsons had gotten in a new batch of 15-22's, so I contacted them and asked if they could give me the three letters of the serial numbers. I had them check the models that I am interested in...the threaded barrel model, the unthreaded model and the Talo model. They have an approximate total of 224 rifles available as of now. The serial numbers are DTU****, DTX****, DTZ***, and the latest one "DUA". I have not seen a DUA reported here, so I believe that DUA should be the most current model, and IF S&W has started to produce "latest spec" models , then a DUA gun may have all the fixes incorporated in them. Several if's and assumptions here I know. I also know that at one point S&W said that one could not predict whether or not a rifle would have problems by the serial numbers, but that may not be true now.

I am going to run by my local gun store- tried to go yesterday but got tied up-and see if they have gotten any new stock in with the DUA numbers. If not, and if I decide to buy one now, I'll have them send me the DUA with the highest number. I think one can request this, or at least I know it has been done in the past.

Interesting fact that I turned up with all my poking around here: This is of course taken only from this forum. As far as I can tell from searches on the posts here, S&W 15-22's have the following letter prefixes:
DSZ, DTA, DTB, DTD, DTE, DTH, DTM, DTX, DTU, DTZ, and now DUA. There may be some others, but these are what my search turned up- although I swear that I remember seeing a DTY and a DTW, but maybe I just lost another brain cell.

If we use just the ten prefixes I found, and assuming that the numeric range in each prefix is 0001 through 9999, and not counting the new DUA's, S&W has made at least a hundred thousand 15-22's. That estimate is probably low, since we usually get posts here from those with problems, and everyone doesn't have problems, so a prefix different than the ones I use here could be out there somewhere. If one counted the number of failures reported in this forum the percentage of failures of the numbers made has to be very small. It would be real interesting to know if the number of failures is going down.