B2 visa extension while parents in India

Hi,
I am in US and my parents in India. Their B2 10 year visa expiring in Mar 2022.
I heard it is better to extend beforehand, rather than be in situation to apply fresh again after visa expires.
Can I file for their visa extension now itself using Dropbox facility in India, now that less than 6 months remaining, or how early can I apply? Due to some personal things, may get very busy as I get closer to expiry date, so want to take care of this now itself.

Also, their travel plans not yet made, will probably be in later half of 2022 or 2023, so cannot provide any travel itinerary, would that be fine? Or any ideas to address this?

Any response would be really helpful.
Basically want to understand whether we can apply for parents’ B2 extension while they are in India and about 4-5 months remaining for B2 visa expiry?

You should be able to apply extension.

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