The coating difference is between the Series E-version and the standard AIS version?
Series E-version is single coated and AIS version has the standard multi layer coating Nikon used at that time.
The long nose 1.8 version which is made of metal also has the Nikon multi layer coating.
The two pancake versions the E-version has a higher weight as there is a alu-part which is plastic on the standard AIS version (at least on the one I have).
But I have heard that the E-version is cheaper made internally. I have never disassembled them :-)