After a long summer break, it's easy to forget most of the things you have learnt even if you can remember the general idea or know that you did learn something about this in your first or second year.
During exam time, you can be super focused and may cram information into your short term memory, which can help you pass exams, but not everything may go into your long term memory.
So it's perfectly normal to have to revise things again from first or second year, and in theory the more you go over things at different times, the more likely it is that you will retain that information.
Hope that helps,
Oluwatosin – 3rd year student – University of Huddersfield