During event and participant (bib) transfers, if the original runner had a Large Shirt reserved and there is no more inventory of Large, the person they are transferring to can claim that Large shirt now. Previously, it showed the size as being sold out.
This also works for people transferring from say the Marathon to the Half Marathon.
Note, this only works for Giveaway options that are the same! So if there is a different giveaway event ID for the Full and Half Marathon, then it will work off the new event inventory.