Discount or not / solved

Hi guys, need your opinion. The curriculum in Reading 6 says, for pure discount instruments, that the holding period yield is the dollar discount divided by the purchase price. Does this definition still hold if such security is sold before maturity? I thought discount can only mean the difference between nominal value (paid only at maturity) and the purchase price.

UPD Oct.19: Solved. As i understand, HPY, as opposed to HPR, only relates to the expected return if held to maturity.