H1B extension approved with a gap of 64 days between new start date & old expiry date

[Stony]

Hi,

My H1B/I-94 expired on Jan-31-2015. My employer applied my visa extension on Nov-6-2014 in normal processing time. But i received RFE on Jan-7-2015.

so my employer responded to RFE by converting it into premium processing on March-19-2015.
Petition approved on March-31-2015.

But email shows Petition approved validity starts on March-23-2015. My old visa expiry date was Jan-31-2015. There is a gap of 50 days between my approved visa staring date and old expiry date.

Can this gap valid ? Will this create any issues in my next visa extension process?

Please help me on this issue,

Thanks!!!