Personally, I do not do the shoulder all the way around. The key is a combination of the tang's taper, and making a tapered hole in the guard material so that it's forced to "press fit" on.
I could try to explain it here, but would be typing all day..... At KnifeMakerTraining, we have a video available on it.....
https://gumroad.com/l/edoIE
Something that popped into my mind, which I find most don't think about....the amount of pressure you use when filing. Bear with me here.... if your file guide is the same type/size as mine (I got one from Bruce too), the carbide slips are only 3/8" wide, and with a knife in there, the total surface MIGHT be an inch...... and a file WILL flex.... so if you're putting a lot of down pressure when you file, the file is likely slightly bowing, you think you're done, but you need to keep filing with minimal pressure util the file simply not longer cuts anything. I mention this because I've seen it time and again.
Something else that happens also is that most file the guard shoulders prior to heat treat....well, when you heat treat, the steel moves....however slightly, it moves, and it's often just enough to throw off a guard fit. You'll wreck a file or two, but post heat treat, if I can't get a guard to fit "right", I will put the file guide back on the blade, and slightly recut to near finished on the disc grinder.....then finish them up with a new file.....one time of doing this = 1 file.
(here's a hint..... Home Depot files are warrantied for life....even for going dull)
