You are correct in terms of apparent inconsistency, but as ever one needs to be wary of multiplying a series of anecdotes and pretending it's data - it's not, it's just a heap of anecdotes.

The CCR desk, like the other Customer Service desks, can handle ticketing alterations. And can rebook people on to other flights. As well as operate AUPs, change seats, "link" PNRs, arrange mobility assistance and so on,.

The problems that get in the way of that are multiple and this leads to this feeling of inconsistency. So out in the real world, very few people understand the critical difference between a revalidated and a reissued ticket. Nor the concept of Airport Control, nor the related issue of Ticket Ownership with linked coupons. Or the structural differences between Commercial and Redemption tickets. Then there is Amadeus versus SABRE versus Travelport. There are ticketing staff in LHR, out of the public sight, in the ARC team.

If something just needs revalidation, so you are on a Commercial ticket and you just want to go on the next flight rather than the booked one, and if this isn't massively problematic from a revenue protection point of view (or something like a weather waiver is in place), then the CCR desk can do it. Ditto the same desks in the First, Club and public areas. However if there are mass irrops and a revalidation isn't going to work, then there is no way that ARC can handle thousands of passengers, and that's the point that people are asked to call the Engagement Centre instead.