Don't assume that because one model doesn't have a button on its remote for a particular function that the unit won't respond to an IR code for that function. Often CE manufacturers will share software development across several models, and they'll all respond to the same codes.

For example, Sony TVs respond to three IR codes concerned with power - there's the usual 'toggle' which is sent by the remote, plus a code that switches it 'on', and another for 'off'. Very useful in macros. They also have codes to go directly to a given video input (e.g. 'select video 3') although remotes that come with less expensive sets often only have a button for stepping through the inputs in a loop.

It's common for similar models launched at the same time to share a 'common parentage'. From what I remember, the 939 and 828 weren't released at the same time, but there's still a good chance that Tim is correct.