I know her

[Wickerman]

I suspect that has more to do with the police wanting Hutch to positively identify the woman he supposedly saw with Astrakhan man as a match with the dead woman (Kelly), rather than it being about any doubt over Kelly's identity.

Exactly, more to do with confirming Hutchinson's story than identifying Mary Kelly.
The police had already been advised that Mary could have died between 1:00-2:00 am by Dr. Bond, so naturally they need to be sure Hutchinson was not mistaken in who he saw.

[Michael W Richards]

I suppose an element of doubt is introduced by the fact that the police wanted Hutchinson to ID Mary after the inquest - can't quite see the point of that.

It would seem Robert that they hoped to get some tangible evidence that Hutch at least could recognize the face. They had confidence that it was Mary from earlier ID's, so it certainly wasn't for confirmation of that fact.

There are 2 witnesses in this case that muddle up the truth, Hutch and Maxwell, and to my knowledge we have no supporting evidence for their knowing Mary at all.