In both subsections(2) and (3) of section 18, there is a common power that the controller has i.e to insert a reference of the prior art in the applicant complete specification. This occurs in cases when the applicant during the time of his/her patent application was not able to know the prior art because the prior art was published on (or) after the new applicants patent application. So there is no way the new applicant would have known the prior art.
Prior art which was PUBLISHED on (or) after the new applicants patent application as per Subsection(2) was APPLIED FOR PATENT AFETR the Indian act 1970 came in existence i.e AFTER 1970.
Prior art which was PUBLISHED on (or) after the new applicants patent application as per Subsection(3) was APPLIED FOR PATENT BEFORE the Indian act 1970 came in existence i.e BEFORE 1970 (during the existence of British act 1911)
You are right that ‘before or after 1970 act’ is not mentioned anywhere in section 18(3). The language used in the act is not straight forward. The answer which I mentioned previously is after going through other sections of the act as well, after which I got to know how ‘before or after 1970 act’ has come in the picture of 18(3). So I recommend you to note down your queries and go through the complete act after which there’s a huge possibility that you can figure out yourself which may take serious amount of time.
Else I recommend you to subscribe to Lexcampus courses where you can get all the answers. Thank you.