In reply to Grahame N:
At the time, the expectation was that the guidebook writer would climb every route or, if this wasn't possible, that they'd at least climb the hardest routes and the most perilous. Thus the onus of guidebook writer would generally fall to the best climber in the area as the person best placed to do this.
Accuracy was prized. It was very much in people's minds that inaccuracy might lead to dire outcomes.
It really was a labour of love. People gave their all. I can imagine Marshall, in particular, wanting to know he'd done the best job he could for fellow climbers.
Mick