pob is preorder benefit, which are photocards. These days you can get them not only during preorders as people call any non album or non lucky draw photo card a pob. Mostly the websites ship them out randomly and one per album bought, the sale for these is always limited
gom open gos for these because although the stores send them out randomly, if the purchase is a division of the number of members in th group then they all send out in sets so joiners will be able to get the member that they want
*keep in mind that stores rarely promise this because even though they usually do it they might make a mistake and without a promise there's no responsibility so the gloms won't be able to do anything about it