H1B Amendment date earlier than original H1/I-94 date

[Sumit Sardar]

Hello Experts,

I have H1B VISA and i797 for client 'A' till Sept-2015. I-94 expiration date is also Sept-2015.
My employer has filed amendment for client 'B', and got amendment approved for client 'B' till December-2014. but my LCA for client 'B' till Sept-2015.

My question is, can I continue working with Client 'B' till my I-94 expiration date that is sept-2015? If not What are my options.

Thanks for you quick help on this.