The forum has no place for such requests. I asked Logitech support to add the DSM-312. I got back a form response which expressed sorrow that I was dissatisfied with the remote, which I never said, and otherwise took a rather defensive attitude. I do software tech support for a large company and I'd be embarrassed if I ever sent a response like that to a customer.
Apparently the way it works is that if someone manually adds codes for an unknown device, they add it to their database. Sometime between the first time I tried it and the second, it "recognized" the entry of DSM-312 but gave me complete nonsense for remote codes. I suspect someone else entered these and gave the wrong device model.
It isn't really that big a deal to add the codes manually for the small number of buttons on the remote and I have now done that. I've generally been very happy with the Harmony remotes and this is the first time it has missed as device for me, but I admit that the DSM-312 is new.
I wish that there was a more comprehensive manual for the DSM-312, but I've managed to figure out the more obscure parts (such as the Settings pages.)