Future I797 - Stamping experience India

[futurevisa]

Friends,

Here's the case, I have 2 I 797 currently.

One with start date in mar'2011 and end date in mar'2012

another with start date mar'2012 and end date Oct'2013

Question is - if I go for VISA renewal now - how long a VISA I am eligible for? (I read old posts saying you can go unto 90 days in advance etc - but there is no such rule - helpdesk confirmed the same)

Did somebody has practical experience of this, where consulate granted them 2 year VISA based on future I797? (or a case where VISA is granted only until current petition end date)

Would appreciate any help in this