Exit stamp on passport - L1 passport holder

[mathewrond]

Hi,

I had an approved L1 petition to stay in US until end of October 2016. I traveled to Canada by road in mid October 2016 via Niagara route. There was no check at the border and I did not have any exit stamp in my passport.

Question - How does USCIS know I have exited US before my I-94 expired? Do I have to explicitly tell somone or send a copy of my I-94 to USCIS?

Thanks,