Time limit for issuing notice u/s 148

No notice under Section 148 shall be issued for the relevant Assessment Year:
(a) If 4 years have lapsed from the end of relevant assessment year, unless the case falls under following two categories;
(b) If 4 years, but not more than 6 years, have elapsed from the end of relevant assessment year unless the income chargeable to tax which has escaped assessment amounts to or is likely to amount to Rs. 1 Lac or more for that year;
(c) If 4 years, but not more than 16 years, have elapsed from the end of relevant assessment year unless the income in relation to any asset (including financial interest in any entity) located outside India, chargeable to tax, has escapsed assessment.

But Rahul jee, notice is ISSUED before the prescribed date. And AO may be having proof also for having issued. Service of notice in April will make any difference?

ao issuing notice as on last date, its not mention that it should be deliver. if you received in april thn also valid

I think service of notice is important

sec148 starts with issue of notice and service of notice is irrelevant.Also see sec149 which lists the time limit of issue of notice u/sec148.

And if the assessee has not rec'd any notice dtd 31.03.2018, but has rec'd reminder notice dtd say 01/10/2018 quoting the reference of original notice dtd. 31/03/2018, then proof can be asked from A.O regarding the original notice ?