I live in Liverpool but grew up on the Wirral and frequently am told I'm a big Wool, and I understood it to be nearly anyone in merseyside but not in Liverpool and plazzy to be anyone not in merseyside but affiliates as a scouser.
To me (from Wales, living in Liverpool) a scouser is anyone with a scouse accent, a plazzy is anyone with a scouse accent that lives outside the L postcode but within Merseyside.