That number feels a little low.
When I went through LHR on Sunday - I got a look at the 'premium brief' sheet.
There were 81 premiers expected through - which I understand includes CCRs (to have 81 prems on their own would be astounding).
So to have 81 through on one day out of 500-600 feels like a high percentage.
(And the other numbers were 1980 for Gold, ~2200-ish for silver and I didn't see bronze before I was spotted snooping).