As we know there is always a lot of speculation around the exclamation point. My experience is based on observation. No no I have not solved the issue but at least I have two examples below with similar dials and close serial numbers. Below you have the two examples the 5512 with the exclamation has a later serial than the one without. They both have 1961 ( correction made I was in error details below) case backs but the exclamation has papers indicating that is was sold in 1963. So the non exclamation has a 66x,xxx serial while the exclamation point has a serial of 69x,xxx within 30,000. 
And a second shot. 
So what does this add to the conversation or what can we deduce from these two gilt 5512 chapter rings. I guess we could say the exclamation came after the to meet some kind of regulation which seems to be the consensus among collectors. It also seems like 1961 seems to be the year most often associated with the exclamation point while 1963 is associated with the underline. No major revelation but an observation between to very close examples.
The second observation is the difference in the position of the serial number. People often wonder what was the correct time period for the change between the serial position above / upper position or below. Again as we can see the earlier serial 5512 with serial 66x,xxx has the upper as can be seen in the picture below with the serial of 69x,xxx has the serial at the lower position. So again what does this observation tell us that the switch most likely happened in or around the end of 1961 beginning of 1962 Why the change is anyone's guess.
As can be seen below the serial is on the upper side of the case. So if you get asked the question when was the change you have the info here.
Bill