Why is this version definitive?

This version of Oliver Twist is considered generally to be the definitive one. But why is this?
Taking the 1982 version as an example (I could take any number of others, but 1982 was the first one i saw), it makes a huge cut form the book by proceeding direcvtly to the burglarly soon after Oliver is introduced to the thieves.

But Lean's version eliminates the burglary entirely, and Oliver's aunt is not even in it. He also has a scene near the end where Sikes takes Oliver hostage while attempting to escape. This was not in the book. In the 1982 clive Donner version, Brownlow is Oliver's great uncle. Lean's version makes him Oliver's grandfather. Neither is canonical, as Dickens never established a familial relation between Brownlow and the Flemings or Leefords.

So why is Lean's version definitive, and Donner's isn't?

Maybe it all centers around Fagin. Guiness's Fagin is certainly nearer to Dickens than George Scott's is. But if Guiness's allegedly offensive protrayla of Fagin is indeed the best, as it may be, why do ll the subsquent versions of the OT go out of the way to make Fagin sympathetic (and they do, I've seen them)? Why not play the character straight, and not bother about being PC?