There was a thread or two some time ago about getting the purple dye out of T-grain films. At the time, I think I remember saying something to the effect that I had noticed this intermittently, and that sometimes it came out and sometimes it didn't.
Anyway, just yesterday, I developed 8 sheets of film in my trays. All were Delta 400, loaded at the same time from the same sub-packet (the sub-packets are the 25 sheet individual packets in a 100-sheet box of film). All were exposed on the same outing, all were developed in the same developer at the same time for the same duration, N+1. Seven of the sheets came out with no purple; one of them came out with a lot of purple still on the film. Go figure.
I theorized (logically, I think) that if I re-fixed and ran it through the washing aid again, perhaps it would come out. I did, and after a five minute wash, some of the purple came out, but not all.
I'm about to conclude that Ilford's coating processes were not consistent. I can't think of anything I did that could account for one sheet out of eight coming out different.