on the e-Ticket itself, there are two dates
the date of Issue - which I have not ever had more than a day or two out from the day I actually booked
the date of payment - and the credit card one might have used to pay for which one might have a monthly statement or the very least an online portal to check the date logged by the CC company
Now, while this isn't QF internal system (which may have several dates logged on a ticket (including PNR creation date, payment date, ticket issue date and perhaps a couple of others (especially if there's subsequent changes - lets not get started on GV's or FCs or TravelPasses etc etc etc) the question was about a relative "cleanskin" situation/
if that's the case, knowing the dates of the campaign, and as long as registration occurred, then if one of the various dates falls within those dates, then you'd like be able to deduce DSC or otherwise.