H1B got approved and RFE also cleared in October 2015, but VISA stamping not yet done. How long it is valid

USA H1B Visa
1

I got approved h1B, RFE also approved but stamping not yet done, how long H1B is valid. Is it valid if I move from current employer to another company? I am living India

2

Please answer to my question

3

Another employer can file a cap-exempt petition for you within 6 years of original approval date.