Vorro, you magnificent SOB! These are great so far. I was wondering where you'd got off to; good to have you posting again!
If I'm not mistaken, one reason for unusual graticule orientation may be to most effectively center/orient the region being mapped on the piece of paper. In the Tzallrach one in particular, if vorro was to horizontally/vertically square up the graticules with the paper's edge, he'd have large zones in the southeast and northwest that really aren't the main focus of the map and would contribute nothing but dead space to the map. With this orientation, only the essential zone/area being mapped is shown and one can still get a sense of direction from the graticules.