The mysterious "corner aręte" is not in either of the Baxter guides. Perhaps it was in the old Blue Grampians guide which I don't have a copy of.
There are 3 obvious short corners L of the main overhang. The first, which I assume is Tequila Sunrise, does appear to involve climbing a corner and aręte, but looks quite hard and poorly protected. The next leads into a dirty groove but you would not head “Up and diagonally right to cracked groove” as the P4 description says from that start. And any pitch starting up this feature looks like a shocker. The 3rd break is much harder than 13, Jerry failed to lead it and had to retreat off gear. I lowered him down from above to retrieve the gear and he couldn’t even get up on a toprope. As you say that whole top wall is pretty hard to make sense of. Fear and Loathing and Desperado must go up it somewhere. Jerry was probably on the top pitch of F&L. None of which helps with identifying where the top pitch of Mug’s Alley actually does go. I have added the top pitch that Jerry and I did to the ACA description. Its a bit of a combo of Holocaust and F&L and at 14 about the right kind of finish for the route.