Please don't edit your post, but add new ones if needed!
What is the meaning of this sentence? Could use multi accounts? Clear it!
It's hard for the people who manage this giveaway if they need to look back 20 pages each time. Now they only have to check the last pages and edit it in the spreadsheet.
That pretty much sums it up - if people would edit their posts (i.e. because they've written their username wrong) we would have to go through each and every of the now >400 posts on each iteration of the spreadsheet, which would make the whole process a lot slower resulting in fewer updates for you.
And no, as stated in the OP multi-accounts are not allowed. If we would spot someone trying to do that we would have to remove all of the used accounts from the giveaway...