Lateral adjustment screws on Challenger Rebate hinge will not turn clockwise, or anticlockwise!?

[super domestique]

Hello!, I am trying to pull my upvc door back towards its frame, but the lateral adjustment hinges (all six of them, two per hinge) will not turn either anti-clockwise or clockwise. All hinges and screws are adjusted similarly, with the marks pointing to the frame (see pic)
Could all six screws have seized or broken? - the door does get blown about in the wind a lot, and it dates from 2005ish - or I might be missing something basic.
The screws for vertical adjustment and compression turn ok.
The instruction sheet I am following https://www.justdoorsuk.com/downloads/challenger-butt-hinge-adjustment.pdf doesn't say anything about the grub screw in the middle of the hinge - is that important?
Perplexed

 

[crank39]

The tiny grub screw is just there to hold the pin in place, often they aren't tightened and the pin starts rising up with the constant opening and closing of the door