The criteria for JEE Advanced set NTA (National Testing Agency) is that a Candidate can attempt examination at most two times in two consecutive years. Candidates should have qualified the Class XII Board Examination (or equivalent) in the previous year.

Hi ! Yes obviously you can appear for JEE advanced 2020, if you give the passing date of class 12 as 2019. Then only it will work. Also a class 12 marks has whole life validity and when you are appearing for a board for once again, the old is generally ignored. So hope you understand and best of luck to you.