B1/B2 Visa and I94 extension

[VSingh]

Hello,

My parents came to USA on visitor visa(B1/B2, valid for 10 years). They got their I94 for 6 months at port of entry, which is ending in november 2017. In between their stay in USA we went to Mexico for 4 days and while way back to USA at port of entry they got their new I94 till March 2018.

My question is, can they extend their stay in USA till March 2018?

[newacct]

How long they can stay on this entry is what they were given on this entry; how long they were give on the previous entry no longer matters.