On mine the serial number is between the nut and the damper.

"Is the number (stamped?) on the aluminium 'beam' or on the headstock? If it's on the beam I suppose a clue to sequence would be if the serial number itself is anodised?"

My former Railboard had the serial number on the top front of the headstock.

The location I mentioned is on the beam. I kind of thought I had previously seen it elsewhere as well, perhaps on the headstock, but when I examined it to answer this question I only saw it between the nut and damper, and I did look on the headstock.

On the other hand, I'm not very observant, so I might have missed it.

Thank you. I think I can just about make out a couple of digits (28, which would make sense) on RC's 4th image?

Ah, yes - stamped between the head and the damper strip.