i know i brought this up already way back in early 2009. Pinoynotes is making an extensive effort to catalog all serial prefixes that have a 2008 A date. They only appeared on 2008 20 peso bills. mostly with the prefixes between XA-XZ, YA-YZ, ZA-ZZ, A-Z, AA-A?
it's a difficult sell right now since it's still in wide circulation. but if you have the patience and if you can set aside crispy notes, years from now the series should be well sought after.