"So we know Hillary had one in 1953."
Yes that's just based on him getting on having had one for the 1952 Cho Oyu expedition, which in turn is based on the fact that the number of watches Rolex gifted / loaned (and it looks like you are right about the gift rather than the loan) to the 1953 Hunt expedition minus the numbers of members who'd been on the earlier one. Some conjecture there for sure.
It's based on this:
"As you know Rolex in Geneva wanted a Rolex on the summit of Mt Everest and they supported the Swiss 1952 expeditions but they also sponsored the British 1952 Cho Oyu expedition as well. In 1953 Rolex again sponsored the British but John Hunt felt it was unfair (on the other expedition members or perhaps Rolex) that the Cho Oyu expedition members should get a second Rolex so only the 1953 members who had not already been issued with one got a Rolex in 1953. That explains the numbers of watches that Rolex sent to the British expedition in 1953.”