Here are some comparisons of the current runs of the Avair P&a and the Grid Stamp Avair:
I have only been playing for a short while and I am not versed in all things Avair history.
The Avair P&A has a lower shoulder with a flatter top than the Grid Avair.
The Grid Avair has a slight upward flight plate. Just a little rise not domey.
The PLH on the P&A is just slightly higher than the Grid Avair.
The wing or edge of the disc (where it fits the hand) has an angled edge like a Mako, Skeeter, or Dart.
While the Grid Avair has a slight bevel/curve on its edge.
Plastic wise the Avair P&A feels like DX plastic that is moderately firm but, not overly stiff.
The Grid Avair is a very firm feeling plastic, the flight plate is more solid. This disc doesn't give too easily when it is flexed from the edge to edge like a taco.
I will try to snap some profile pics and post them tomorrow. Hope this helps.
Clearly. It's spelled Aviar.