Hello meet, congratulations for your result. 

The GATE score is vaild upto 3 years. You can use your score for admissions into masters courses but i as far as i know the for PSU's the recent GATE score is required.

I hope this helps. All the best.

Hello Meet

If you have written GATE last year and again this year, both the cards are valid for admission. You can use the one with better rank and join M.Tech. Better AIR rank is preferred. Don't worry about it.You have many chances.

It is wholly upto you which one you are going to use to apply.