Did I overstay? Dropbox vs In-person ineterview

[Rocky86]

Hi,
I came to us on H1b in 2016, subsequently my h1b was extended feb 2017 until feb 2019. I also got i 94 validity until feb 2019.

In Sep 2018 my H1b extension was again approved for until feb 2022.
I traveled to Canada in Dec 2018, while returning I did not produce my approved extension and immigration officer too didn’t ask for it and issued a new i-94 with validity until Feb 2019 based on my previous approval/Visa.

I was under impression that since I have approved H1b extension I can stay as long as I want and will need stamping only if I travel to any country other Canada & Mexico.
Couple of days back my employer during routine verification found that I am staying out of status, reason they gave me that i94 that came with my extension was overridden by i94 issued when I came back from Canada.
I have left US immediately, and currently in home country.
My question is did I overstay?
If yes, Should I go dropbox or in-person interview for Visa stamping? I feel I can explain better if in-person if consular needs to know the reason why I overstayed

Please suggest.

Thanks.

[Mogu]

My understanding is that your employer's attorneys are correct. Your stay was regulated by the latest I-94 that you got while coming in from Canada.... so long as you were issued a new I-94. I know I never got new I-94s when reentering from Mexico.

You should explain in-person. I imagine even if you try dropbox, you'll be summoned for an interview.