OP has not specified a carrier, so without specifics, you get a general answer.

First, presuming that the carrier uses bar-codes or some other form of coding, anything written on a BP is simply window-dressing. The BP is certainly coded for a specific flight departing a specific airport on a specific date.

Second, few if any carriers issue BP's more than 48 hours in advance. Most no more than 24 hours. Thus, no matter when you purchase a ticket, the BP is good for a gflight in the next 1-2 days.

Last ---- General rule of thumb is to populate only those fields required for the piece of paper (and we're talking about one of those) in question.