[OJFord]

Well presumably there's no accepted concept of a 'pole'. (If there were, yes I'm sure the Antarctican Flat Earth community is adamant it is the inverse of the above link..!)

But, generalising, 'where is the centre', I don't know.

Back in the day they presumably didn't claim to know, because obviously nobody had reached the edge, so there was just known area, and unknown beyond it, in every direction.

[arethuza]

The Charlie Stross story "Missile Gap" has a literal flat Earth and just that "and unknown beyond it, in every direction"... The 'Earth' there definitely doesn't have poles.