if you follow an NPC's wake their state is persistent, always. you can follow an NPC for hours if you want across the galaxy slowly picking it apart piece by piece. for this reason i always carry a wake scanner. if an npc scoots away just in time to save itself i follow its wake and catch it while its shields are still recharging.
one of my favorite bounty hunting tactics is to ambush an anaconda or corvette in a high sec system. it will jump when its gets to low hull successfully almost all of the time. then i follow it and finish it off one on one while is has no shields, busted modules and hull down to 20%.
I'm aware that using the wake scanner enforces persistence, but the situation I'm talking about is when they are pursuing my CMDR.
Sometimes one of my trade ships will get pulled and I'll not have sufficient weapons equipped to destroy the NPCs quickly, so I'll disengage. When the NPC shows up a moment later in SC sometimes they do retain the damage I've dealt to them, sometimes they don't.