Mismatch between GSTR2A & GSTR3B

yes there  is a mismatch 

For FY 2018-2019, ITC Claimed as per GSTR 3B was Rs 425000 whereas as per GSTR2A it was Rs 360000

But the official notification came in OCT 2019 , will it be Applicable for FY 2018-2019?

It is better to consult a professional on the  issue. 

The notification says that "1. ........  (2) Save as otherwise provided in these rules, they shall come into force on the date of their publication in the Official Gazette. "

In view of the same, 3rd point of the amendment does not specify a particular date which means that this cannot be applied with retrospective effect. Fir retrospective effect of this notification specifically it has been mentioned in the rules which amendment would apply from 1 July 2017. 

Hence, this specific amendment in the said notification number 49/2019 – Central Tax date 9 October 2019 would be applicable from 9 October 2019 which is prospectively.

Disclaimer of Opinion:

This is just an advisory in general terms which cannot be referred by you for representation to the Authority. This is only for your understanding. Please refer a professional advice in this regard if the same is to be referred for representational purposes.

Thank  you all for the response