In the present case, since he has been given promotion ( I am afraid how an employee against whom a disciplinary action has been taken is given promotion) there are two possibilities. On promotion whatever increment is payable to him will be paid only in 2019. Now since he has retired from service, he should have retired with a basic pay of 2016. In pensionable salary also this increment will be on hold but now the revised pension based on basic pay of 2016 plus two increments will be released.
The above is not a conclusive answer because I am not okay with government service rules and their fixations. Therefore, I invite others to put their comments on this issue.
13th June 2019 From India, Kannur