H1B extension calculation advise needed

[anagha.blr87]

Hi,
First time when my H1B got approved, I got my I797 approved from 02/07/2016 to 09/16/2018.i.e. for 2 years 7 months, 10 days
I got my visa stamped on 05/10/2016 and the expiration date stamped was 09/16/2018. i.e. for 2 years, 4 months 7 days

When I applied the H1B through the 2nd employer, I got my I797 approved from 04/14/2018 to 12/13/2020. i.e. for 2 years 8 months
My visa stamped had validity till 12/13/2020.

Looks like my second employer while transferring H1B, did the H1B extension also, though my old H1B hasnt yet expired.
Hence there is a overlapping of 5 months between above 2 I797 approvals. Can I reclaim these months?
How much is left on my H1B now?
By looking at both I797 approval periods, after current expiration date, I am left with 8 months to reach the 6 year term. Am I correct?
Also I arrived late by 7 months to US for the first time, can I reclaim these months as well?
Please advise.

Thanks

[R78]

Keep the visa stamping out of the calculation.
H1 is granted for a total of 6 yrs (3yrs max each time).
Only time spent in the US on H1 is considered towards the total
Any unused time (outside the country) can be re-captured only if it is requested at the time of filing / extension.
To get an accurate count, look at the entry / exit stamps on your passport and only count the days you were in the US, and minus it from 26280 (6yrs)