Discoloration on lower back is presumably from having another card stuck to it in the past.

The 1999 NBA Upper Deck Black Diamond Single Card #70 featuring Tom Gugliotta from the Phoenix Suns is a highly collectible sports trading card. This original card manufactured by Upper Deck in 1999 is part of the Black Diamond set and is a standard size card made of card stock, paper, and plastic. It is a base set single card with an insert, representing the National Basketball Association (NBA) league. With its unique design and limited availability, this card is a valuable addition to any basketball card collection.