damson tree variety

[blight]

my damson tree, that i bought a long time ago in england is on its last legs.
the odd thing about it is, that a root sapling, that i left to grow for propagation bore
tiny  yellow, flavourless plums,  looking very much like thefruit of  rootstock they use for grafting plums on.
i always thought damsons came true to seed.
so, how are damsons propagated then?
and are there different sorts?
thank you.

[blight]

[Obelixx]

There are several different kinds and I expect they are propagated by grafting onto rootstocks.   The RHS plant finder lists several kinds, including two with an Award of Garden Merit.