I am so onboard with your thoughts. I wish I'd paid more attention in high school english class & could be more authoritative. Bad grammar, spelling, sentence structure etc. in published work bothers me to no end.
When I correct others, my wife takes issue & calls me annoying. I like to think of it as being helpful.
So haunches are the wider shoulder, and "tongue" is what I am calling the part that gets notched. One gets notched to run high and the other low. The mortices will intersect and create a hole that turns the corner. Leave the high "tongue" a little wide so that it hits the low. Trim it until it just misses the other. Don't try for a perfectly measured cut. Cut it big and sneak up on the fit.