hello,

GATE is valid throughout our India until you take up your next GATE exam for better score.So try putting your 2017 GATE score for the colleges you are interested.As you have mentioned Karnataka colleges,even they ll take students based on GATE and no need of taking dedicated pgcet exam again. BUT,In the least case, if they insist (only if you don't meet the required criteria eligible for getting admission into those colleges),then you may have to.  

hope this helps :)

thanks and regards,

SIRISHA SANATHA.