H4 visa - length of stay - match H1B visa stamping or I797?

Hello,

I had my H1B visa approved in Oct 2017, till May 2020. I had my visa stamping also done with an expiration date of May 2020. Recently, I moved job locations and applied for a H1B amendment. The approval notice I797 for this amendment shows my validity until Dec 2021. I haven’t gotten a new visa stamping since.

Now I am filing for my wife’s H4 visa. In her DS160 form, should I use May 2020 (my visa expiration date) or Dec 2021 (my latest I797 expiration date) to calculate the intended length of stay?

Thanks

Fundamental: Your passport stamped visa is useful ONLY to enter into United States, after that it got no role to play while you are inside United States. All you need to care about while inside united states is your I-94 date. So, use your latest approval (which gets an I-94 at the end of that approval notice) and get H4 approved.