Amendment V/s Extension - Which expiration Date can be considered as Legal status, such as not Out of status?

[ImNotAnAttorney007]

Hello H-1B Friends,

Would someone help me for my situation by answering my question so that I can take  a right decision.

1. My H1-B EXTENDED petition is valid until July 31st 2019, and also that I-797A has I-94 enclosed with it which is having expiration date July 31st 2019. By this date I will complete 6 years of stay on H1-B with out GC processing filed.

2.  My H1-B AMENDMENT  petition is valid until Mar 29th 2019, and also that I-797A has I-94 enclosed with it which is having expiration date April 9th 2019.

My question is, Which date that I should consider as a valid date to stay here in the US Legally , Is it July 31st or Mar 29th or April 9th 2019? On which date that I will go out of status if I stay here in the United states?

Thanks

Jasunai