You don’t know that the frames are out of spec. according to the contract Fairlight made with the manufacturer.
No we don’t know what the contract says. But my opinion is that a company that is happy to create a 70 page pdf, for a single bike, showing exactly what the customer can expect in terms of, well everything, including tyre clearance, is unlikely to be vague with the frame maker.
Edit looking through the 72 page design notes maybe the problem is them not knowing quite how big some 2.6 inch tyres were combined with some allowed for variation in the spacing.
To be fair 2.4 inch would be fine for me