Dating Orrefors crystal or glass

[ahremck]

Does anyone know of a reference to Orrefors glass & crystal that gives dates for the more common pieces?  The Orrefors Glass book by Duncan gives some details re signature letters and some of the more special glass Ariel, Graal, etc.

Also the book tells you about types of glass:-
Initial followed by letter A for cut glass
Initial followed by letter E for frosted glass
Initial followed by letter U for uncut, smooth glass
Initial followed by letter Z for green iridescent glass

So PA**** refers to a piece designed by Palmquist in cut glass.  But what does P**** refer to?  Does the lack of the glass letter mean that it is crystal?

Ross