Three different "Victoria" plum trees

Between myself and my father, we have three plum trees all bought as "Victoria" plum trees. Of the Two in my garden, one was bought from a garden centre and seems legit (reddish yellow fruits of classic size) the other tree is is a inky blue fruit about the same size and of a reasonable flavour - slightly more "plummy" in taste, this was bought from Homebase, as a Victoria plumb too. My father bought a "Victoria" plumb from another garden centre and got something entirely different again.

How come?

Z