Gillette sold three different Toggles and the first two of those have a Gold and Nickel version, giving a total of five.
There are other versions but they are all prototypes.

Although I had read about the differences, only once I received my Serial Toggle, was I actually able to see and document the differences first hand.
All the images below will have the Serial Toggle on the Left, the Chrome Toggle in the Middle and the Standard D1/F4 Toggle on the Right.
(The one in the images below is my F4 version)
That is Oldest on the left to youngest on the right.

Starting at the top.
They look like they all have the same doors. When we open them we see some differences.
The Serial Toggle has an extended diamond shape recess and the other two have a recangular recess with rounded corners.
The Standard Toggle has a 'toothed" middle plate and the other two not.

Moving under the head to the adjuster dial section.
They all have 9 divisions but the Serial toggle is numbered 1 - 5 and the other two 1 - 9.
If I am not mistaken, the Serial Toggle is the only Adjustable Razor that Gillette sold that wasn't numbered to 9.

Staying in the adjuster dial section:
Both the serial and the Standard Toggle have a Red Dot as the marker, while the Chrome Toggle uses the spring as the marker. The adjuster dial on the Chrome Toggle has a notch that prevents it from been over clocked, while the other two this is dealt with internally.
The other difference would be difficult to distinguish unless you are looking at them together and that is that the knurled section on the serial toggle is wider then the other two.
Lastly, the Standard Toggle has a small flat section under the knurling.

Moving a little down the handle:
There is no crimp groove towards the bottom of the handle on the Serial Toggle and the other two both have one.

Just before we get to the Toggle itself:
This small section on the Serial Toggle is in a very shallow "V" Shape that corresponds with the top shape of the toggle and looks like a close (more finished) fit.
On the other two the top of the toggle itself is more spherically shaped and the fit doesn't look as close.

We now get to the bottom and the Toggle Itself:
The Serial Toggle has a Red Dot on one side. This indicates which side opens for a blade change vs which side rinses. Opening it towards the Red Dot, it lifts the doors and allows water to run through the mechanism while opening it the other way will open it all the way so that the blade can be changed. On the later two, there is an internal ball and dedent that provides these functions, regardless of which way that the toggle is opened.

As already mentioned, the top of the Serial toggle is in the shape of a shallow V, the other two are more shpherically shaped. There is also a difference between the Chrome Toggle and the Standard Toggle. The Chrome Toggle has a "straight" slot and the Standard Toggle has a "circular" cut-out in the middle of the slot. Although difficult to tell until you are looking at all three, the toggle on the Standard Toggle is slightly longer in length than the other two.