Hello , 

As your query is you fail in 12th science in ghs a b both in 2019 and you want to reappear in 2020 March exam. 

I would like to tell you that yes of course you can apply for the re examination in the March of year 2020 from the same boat and of course I want to tell you that even if the old ghs a b syllabus was banned or not but still the question paper for you will be based on the same format or the syllabus that was published for you in this year so you don't need to worry and just prepare for the exam. 

Thank you.