Most editors try to be sparing in their use of exclamation marks. I’m not sure what the quarto or the folio look like exclamation point wise but I know modern editors try not to get too crazy with the !!! The hope is that the words are dramatic enough.
It’s not entirely justified to put one everywhere. This one, this one is entirely appropriate if you want to suggest Claudius’ sense of surprise. The punctuation gives a sense of the astonishment that Claudius must be feeling. But while Claudius may be feeling astonishment, it’s not a forgone conclusion that he lets that astonishment slip. He is a guarded political fellow who (with the exception of watching plays) mostly keeps his cool.
He could probably get away with: From Hamlet.
Or even a disinterested.
The news is surprising to Claudius. Everyone in the audience likely has a sense of that. We might not need to see him astonished to know that he is so. It might actually be very interesting to watch him suppress his astonishment.