According to the part numbers, the registers are the same for Series 1,2,3
The housings are the same for Series 1 and 2 and slightly different for Series 3.
Series 4 had the thinner and wider vents - entirely different than the early ones.
Series 3 is The early L model.
I know Wilkinson does NOT have any series four units.
I think he is also void of the earlier versions, also.
I bought some series 4 from Tara at Hall through eBay a while back. I'm hoping to add them as left and right outboard vents (near the doors) into my Pre-L dash for better air distribution. By measurement, they should fit. It will necessitate moving the flasher and wiper controls, though.
Larry
Here is series 4.