300 years old sounds pretty young lol … I hear the worst ones are either from the times of Babylon or from The Fall lol
I dunno… I’ve studied exorcism, but never had circumstances to use anything outside of the preventative stuff…
In the lore, demons can’t always be kicked out on a specific timeline; they’re there as long as God permits. But, when their time is up, then they’re gone. In most situations, the rite of exorcism does more to torture and restrain a demon rather than directly remove it. But it does do a pretty good job of scaring away the weaker things.
Sometimes the vibe around Exorcist manuals is enough to scare things off…