I've seen splines that were clocked (twisted) 3/4 of a tooth right where they engaged. Figure that one out...? Scratched my head when I pulled them out of my 8.75.....
Axle such as what you described came out of a SG unit. Seen it many times, not that unusual. Old 8 3/4” SBP axles where the splines look good all the way thru the length most certainly came out of a open rear.