My GC1 had wood aprons that were painted yellow with a white base. The skirts were plastic and were to hide the bottom of the pockets.
Here are things I remember when I was dating my table.
GC1 had non leveling legs. Leg Levelers started with the GC2.
Ashtrays were a GC2 option, not GC1.
The casting that holds the rail bolts (underneath the rail) has a certain shape on GC1's. It looks like a circle with a moon if that makes any sense.
GC3's say "Gold Crown III" on a sticker on the base.
GC3's have brass or copper name plates on the rail. I think 2's and 1's had a silver color.
I think apron wood was different. GC1 was made of ASH (I think) and 3's were made of poplar not sure about 2's. My GC1 had ASH stamped in the aprons on the back side.
Under the pocket castings, my GC1 was stamped with a date of 1962. Maybe all pocket castings were also dated. Pull one off and look I guess.
Scorers were different. I know 3's have different scorers than a 1 but not sure about the 2 and I have never seen a 4 with scorers but that does not mean they don't exist. My GC scorers were larger than the 3's. I think Mullers has a pic of a replacement for the 3...
I also think the aprons are bolted on in 3's and 4's where 1's and 2's had a very nice tounge and groove milled from extruded aluminum. A much better system than the 3's and 4's, IMO.
Slate pins is also an identifer. I don't remember the specifics but my 1 had them and other models did not. Maybe it was just the 3's that did not have the alignment pins.
The slate itself was manufactured in Virginia on some models and from Brazil or Italy on the others. I don't remember which.
Please note that all of this is hard to remember so I surely got some of it wrong but if you look up these different things, you should find my mistakes

Anyways, thats all I remember about the differences between the 4 tables.
BTW - I think you have a 1 or a 2. I almost want to say 2 because of the color. As far as I can tell, Yellow, Red, and a light powder blue were the only colors on GC1's and only on the aprons. I think all the rails were the fake wood until 2's came out. Really not sure about that one though. Your color looks to dark to be the Blue offered on the GC1. I hope you have a 2, that's my favorite one.