Service tax input recognition

As per third proviso to Rule 4(1) of Cenvat Credit Rules – Cenvat Credit is not allowed after six months of the date of invoice (Newly inserted by Notification No. 21/2014 –C.E.)

However the above proviso applicable w.e.f. 1st Sep, 2014.  But this issue is not clear whether this proviso is also applicable to the invoices issued prior to 1st Sep, 2014 or not.

But if consider that the above proviso is not applicable to the invoices issued prior to Sep, 14 - then we can take the credit of above said mistake under the following provision:

Rule 6 (4A) of Service Tax Rules, 1994 - where an assessee has paid to the credit of Central Government any amount in excess of the amount required to be paid towards service tax liability for a month or quarter, as the case may be, the assessee may adjust such excess amount paid by him against his service tax liability for the succeeding month or quarter, subject to the condition that the excess amount paid is on account of reasons not involving interpretation of law, taxability, valuation or applicability of any exemption notification.

About Revising of Service Tax Return

As per Rule 7B of Service Tax Rules, 1994 - An assessee may submit a revised return, in Form ST-3, to correct a mistake or omission, within a period of 90 days from the date of submission of the return.

So should I have to transfer such Input to P&L??