I think most of them have the coating, even as far back as the 128k. My 128k has it, I just assumed they all did. Here's a photo of the guts of a 128k, with the coating:http://kcomputerzone.ca/media/gallery/Apple/Macintosh%20128k/Back%20Open.JPG

Click to expand...

That's a completely different coating. That's the traditional gray paint, not the reflective silver coating. I have Never seen the silvery coating in any 128,512, Ke, or Plus (though I've never had a Plus from the SE era). The only Compact I have ever seen this in is the SE era.