Here is one small but interesting scope about Mersal. We presume Vijay is a fan of MGR in the film as you could see MGR's poster not once but twice.

What is even more fascinating is the first MGR poster can be seen when the father Vijay is fighting with someone at a theatre which was screening MGR's classic film, 'Ulaikum Karangal' while the second poster is visible while the son Vijay is taking push-ups at his (Presumably) house.

Another thing that you could notice from this is the time period in which father Vijay lives in (The flashback portion). 'Ulaikum Karangal' released in the year 1976 so we feel that is when the flashback Madurai portion would be set in unless if the theatre had not re-released the film. We cannot rule out the option of a re-release as a lot of MGR movies were screened during his demise in 1987.