Managing offers

Having completed a VS with a large London firm I accepted their TC offer.14 days later I attended a final interview with my preferred US firm and received another offer. I did not see until today that it is stated on the US firm’s website that they won’t interview candidates who have already accepted a TC.

I immediately informed the original firm that I had had a change of heart (who were totally understanding, only 2 weeks had passed after all) and accepted the US TC. I also informed my summer VS and an additional firm from whom I also had an offer that I had now signed a TC so was withdrawing from the process.

In retrospect, I see that I could have managed this more carefully and should have simply asked the VS firm for an extension. Do you think this could pose a problem down the line if the US firm find out I interviewed with them having already accepted an offer? I honestly didn’t know they specifically stated against it and was under the impression that it was voluntary whether to inform other potential employers. I also obviously made sure things were smoothed over with the first firm before accepting the second offer.

Any views appreciated... just how 'voluntary' is the code for students? I'm worried this might later harm me and wish I had been better informed three weeks ago...