State GDP data

[Prk]

Hi all, 

I am sorry if this comes across as stupid but I have a basic question. 

I am trying to get relief/real(GDP) variable ranging 1990-2014. I downloaded the state GDP data but realise that it is given by different base year (2011-2012, 2004-05,1999-2000,1993-94,1980-81). I need a long run series of state income. 

(1) What is the best way to splice/rebase this data? Do I change the to base year closet to the 1990 or the latest?

(2) Also, for those of you who may have worked on this data for research purposes - there was a recent (in 2018) GDP data row regarding rebasing of GDP? To my understanding this is a practice globally and has been done in India as well. Was this just a political row or did it have any academic consequences too?

Thanks in advance

Regards,

Purnima