Thanks, I see this is used on a number of Canadian routes along with a 13.5K C+ level (SSMS135). I've updated my post and added the YSMS080 level that was spotted last year just in case it's out there somewhere. Have yet to see any YSMS035's around at this time (which were available on several intra-west routes last year). Need to look at the fare rules to try to figure out what the difference is between a "YSMK" fare and a "YSMS". I think all the "discounted" (<12.5K) coach domestic levels have a 3 week advance purchase requirement.

Update. I did not find any substantive differences in the fare rules between "YSMK" and "YSMS" fares. They both have a 21 day advance purchase requirement. I also found a YSM100 fare between DTW and MDW. It does not list an advance purchase requirement, however, it looks like they are only available with a 14 day advance purchase.

Also, some partner's have their own fare codes for the different levels. For example, VS TATL flights have

YSMG300 30K
YSMH400 40K

Also seeing some Premium Economy "P" award fares on VS at 55K level:

WSM550 55K