Originally Posted by Mulett:
“Roger Delgardo was the first Master we met . . . not necessarily the first Master!
As mentioned previously, the 'Anthony Ainley' version of the Master (in the 80s) was well versed with The Valeyard who appeared to be a future Doctor . . . so he knew the 6th Doctor at the same time as a future Doctor (an evil version of the Doctor from somewhere between his 12th and final incarnation or something).
The Big Finish productions have Romana meeting all different versions of the Doctor in different orders too.
So I don't think Time Lords necessarily meet in the same time line.”
Also remember that Ainley Master met Doctors 1, 2, 3 and 5 in 'The Five Doctors'
Doctor 11 could meet Delgado's Master by means of clever computer jiggery-pokery, but it would be tricky to expain how he could keep trying to kill other Doctors, having met Doctor 11.
However, as I have suggested once or twice, I could envisage a story much like Star Trek's famous DS9 episode in which Sisko and his people visited Kirk's Tribble tribulations. They even got the actor who played the Klingon agent Darvin to reprise his rôle. Doctor 11 and the current Master (or a new one) could visit, say, Dćmons, each trying to change or restore events without being noticed.