Hi Pete, thanks for your answer. Please correct me if I'm wrong: Does this grade refer to the rarity of the ticket? One more thing: the other tickets in the same grade and in the higher grade are also Beatles tickets?
The grade has nothing to do with the rarity of the ticket, it is strictly about the condition.
The population report is specific about this particular Beatles ticket from this venue on this date. It only includes those tickets that have been graded by PSA. In reality, there could possibly be a box of these tickets sitting in someone's attic, and if they have not been graded by PSA, the population report will not know anything about them.
Different Beatles tickets from other dates or venues would be a different population report.
For example a Mickey Mantle Topps card from 1953 would have one population report while Mickey's Topps card from 1955 would have another.