i agree with what your saying, this pole is only a few weeks old tho..
To be honest all previous poles ive had from gardiners have been fine the odd clamp coming loose which i just glued back on (although i do think the clamps could be improved on as ive found they do need constant adjusting a bit after a while), just this one needed adjusting from the start..i have had something similar before with a couple of older poles when i brought a couple of extensions for a 22ft slx where as 1 of the poles base section fitted into the extensions the other one wouldn't (would only go in about 5 - 6 inches then wouldn't budge) in fairness alex did mention to contact him about it but it wasn't necessary for it to fit both poles so didn't bother.
So i do think that not every pole is exactly the same diameter but i also would think that this would be almost impossible to get every pole the same there must be some tolerance differences to be expected.