I can accept that Vimes physically looks a lot like John Keel but what I don't get is: why is Vimes able to convince people that he is John Keel even though Keel is in fact dead and lying in a morgue? I can imagine that someone from the Watch is aware of this and might have even put him there himself.
Ahem. The only people aware that John Keel is dead are Carcer (who killed Keel) and Ned Coates (who Carcer suborns because he suspects Vimes, but who Vimes later tells about his time-travelling, resulting in Coates changing sides again).
Vimes has changed history, so the world resets into a timeline where Vimes is Peel and Peel is Vimes.
Ahem (again). Keel, not Peel, unless Vimes becomes Sir Robert Peel and founds the modern London police force.
I've been thinking more about this. Peel had only just arrived in Ankh-Morpork when Carcer killed him, so his face was not known. The fact that Carcer had not been there in the original timeline meant that he had not died and young Sam Vimes went on to remember Peel as a different person.
In the original timeline, Keel would not have died and would have taught Young Sam Vimes all he knew about policing. Then Vimes would grow up to be the drunken cop we see in
Guards! Guards!, etc.
The fact that Keel dies in this timeline, however, means that Vimes has to teach his own younger self all he knows, which is a job and a half.
Because Carcer caused a branching in the timeline, Sir Samuel was able to step into Peel's place and thus cause a change in how things happened. When Vimes got back people like Vetinari recognised him at Vimes because they were now in the new, changed timeline.
Vetinari recognises him as Vimes because he knew him as Vimes for a long time, although
in the past timeline, he knew him as John Keel.
Everyone else recognise him as Vimes because they never knew him as anything else.
Like I say . . . quantum.
... and the Monks of History, too. (Lu-Tze FTW!)
