Is stamping required from US consulate as old visa still valid.

Need help with my situation here:

Have a valid H1B stamping with Employer ‘A’ till July 2017 while I travelled to India in Mar 2015, then came back and changed to different Employer B and then changed to Employer C with a valid I797 approved till July 2018.

Planning to visit India next month:

Question 1: Do I need to get stamping done?

Question 2: If stamping is required am I eligible for Drop Box?

Appreciate your help on this.

Stamping is not required provided old visa stamp has not expired. You can return on old visa stamp and new employer’s petition. Remember to use new petition at PoE.