Dear Rashid, your GATE svore is valid for 3 years from the day the results have been announced. So lets say you appeared for GATE consecutively in 2018, 2019 and 2020. But your best score was from 2018. You can use it until 3 years. But you cannot take admission in for a year that already has been done with. So you can take admission in the current year with the past years score.