Just to update desks have moved again!!! as of my visit on 2nd April.
"A" tickets are for Europeans "B" tickets are for non european non Spansih.
Spanish have a completely seperate numbering and appointment system.
As you enter the Extranjeria (turn right after coming through the main Police station entrance) The first desk you come to is still " Information" the whole of the left hand side desks are now for Spanish nationals, at the end of the room there are two desks straight in front at the end (A's - European nationals) and then sideways-on at the bottom right are now the "B's" non Spanish non European.
I think the officers get bored so like a change of scenery every so often
