I think it's fairly consistent… (Doctor Who)
I mean, eh… not really. Doctor Who is my big show, I’m way more into it than Star Trek, but any sense of consistency in it… eh.
There are callbacks, as you mentioned, little clips and so on, but…
It’s clear from the first six years of the show that the Doctor has one heart, until in 1970 he got two.
Regeneration was originally presented as being something which was inherently part of the TARDIS, whereas later it became a natural process (and it took them 5 tries to nail it down into what we understand now).
The Daleks as originally presented originated as Dals and are seen to be a rather limited species in terms of mobility who are content to exist within one city. In their second story they are repositioned as universal conquerors. A decade later, Dals goes out of the window and they became Kaleds originally.
UNIT stories take place in the 1980s… or is it the 1970s?
Doctor Who is a sprawling mess (and I love it for that), because unlike Star Trek it wasn’t driven by one individual for the first few decades of its life. It’s a hodgepodge that fits together only if you squint at it, really hard.
These days, most fans resort to the ‘Timey Wimey’ Moffatism to handwave away the many, many inconsistencies that exist within it. I don’t think it’s comparable to Star Trek in that sense at all.