A nit-picky question here:

So you have a pt with an open wound over his sacrum. He is someone who does not turn on his own, he has impaired circulation and impaired sense of touch/pain, and the wound looks just like a pressure sore (not any other kind of wound)

The wound blanches. So then it is not a pressure ulcer?

But can the injured tissue not become blanchable once pressure has been relieved for a sustained period? In order to heal, the area has to have a blood supply, thus we would expect that the area would eventually become blanchable, right?

Or has it been found that a pressure sore will never become blanchable?

Google has failed me, so I thought I would ask you good folks :)

If it is an open wound on a pressure area, whether it blanches or not, it is a pressure ulcer. Non blanchable intact skin on a pressure area would be considered a stage 1 pressure ulcer, However intact, blanchable skin would not be considered a pressure ulcer but you may need to institute preventative measures.