Hey, sorry for delayed reply!
The questions might be same or similar, but as far as i know, they do some additions everytime, i had bought their series in march i remember, march end, it was pretty decent. Infact there were changes from my initial year too, like they updated some solutions and all that. See there would be very few incorrect questions and that will be there in almost all series, i find theirs more relevant. You could try mock tests of allen, fiitjee and resonance too if you find them free online, other than that i feel doprep is good. They should update stuff too else also you can go by it as there are no changes in JEE or bitsat as such.