I ran a Guest List Report that shows 41 rows of people that purchased tickets, but when I look at the ticket inventory in my event, it shows that 43 have been purchased.
The Guest List report is going to show one Event registrant per row, which means that some registrants who purchased multiple tickets are only going to show in a single row. The Guest List report will also include data from all Ticket Classes. Sort the TC_NAME column alphabetically and add up the results in column NUMBER_ATTENDEES for that specific ticket class. This number should equal your ticket inventory.