I just noticed that K, L and M as the last (materials) letter aren't mentioned at all 

Just checked my Goldeye and it says XGC 801 

I dunno if this has been brought up already, but what does “SRP” stand for in SRP? Sox Roadway Prismatic or something? I’m guessing the US variants are not too different from their cousins.

@ Econolite03 - Not as nice as that. According to AgentHalogens comment on my MA60 post, SRP would mean as follows:

S = SOX
R = Lateral Mount
P = Die-Cast Aluminum (American SRPs were Fiberglass so it doesn't apply to that. In addition, that designation was carried over to the SRP II fixture (the modern AEL version) so it REALLY doesn't mean anything down there.)

Ahh, I see. I never imagined that’s what it stood for. Thanks for the info.

I just found a reference to the Philips naming scheme in Matthew Eagles' book "Why SOX Lights" - what he says is this:

Edit - Ah, I just read the post you linked to, sounds like that could be it.

That is indeed my resource material.

It's a good book, apart from anything else, our Gamma 6 (aka 'Gemma') is on page 81 

My Philips SRM's are labeled for 2x90 watt, but have one socket at the entry side for 1x180 watt. Not sure if all the large SRM's are labelled this way.

One I've seen on youtube is labled for 180, but it is in fact 2x 55. I think the label is what the lantern originally had as the canopy was made. But at some point, either in the factory or in the field, it has been 'rechambered', if you will, to a different lamp size.