You are mis interpreting the data, there were 640 Covid deaths among those who received both doses, not 640 participants. There were also 68,733 Non Covid deaths among that cohort. Not to mention everyone who didn't die.
I'm definitely not saying there are 640 participants, just that the size is unknown. Non-Covid deaths is a poor proxy of the population size, as that population is older because of how the vaccination programme worked. I don't think I'm making an interpretation, just pointing out the unknown
