Can I be able to go stamping if existing stamped visa and new 1797A starting 3 months later?

[sai V]

My Current H1b is valid till 15th Aug 2023, I got the H1b extension approval valid from 16th August 2023 till 7th Aug 2026
I am planning to go outside US From april 2023 to may 2023.But, I have been worrying to do international travel before 16th Aug as there is a possibility that at POE (point of entry) in US, the new I-94 may be stamped only till 15 Aug- As the new extension won't be valid until 16th Aug2023.My attorney has mentioned that i can provide my new I 797 copy to cbp team at POE but i think there might be chance they will extend i94 only until Aug 15. Will this cause my new extension to get INVALIDATED. 

I was wondering if you could advise that at POE if I enter US before 15th Aug will my new I-94 be stamped for 15 Aug 2023 or 16th Aug 2026? Also how does it affect my H1b extension approval what I already have with me.

2nd scenario:
If i secure drop box appointment and go for stamping in India. Will new visa start date be approved date or will it be start date of Aug 16th 2023 and if it is will i be able to enter USA before aug 16th on existing visa or will my existing visa be marked as duplicate and i will not be able to enter US until aug 16th.