It is 25 years to the month of make. Model production has nothing to do with it.
You want a skyline built in 5 of 1991 then it would need to be 25 years to the month.
It seems on most kei vehicles the month of build is always january from my experience as the title is slightly diffeent than the regular cars. Makes it a bit asier to import. but its good to double check with your exporter first.
1965 Debonair Deluxe, 88 starion,78 lancer, 84,85, and 86 ex1800 gsr turbo lancers,87 minicab van estate supercharged 4x4