Index Small If Row Column formula not returning all results

So I have a spreadsheet which should display all students timetables. For some reason it does not return all results. Some work and others don't. I have attached the spreadsheet as it's difficult to explain in words how the whole thing works but basically I type in a class code into AQ3, there is an index array which returns all the names of pupils in that class in AS3:AS11. In column S of the sheet Classes where the raw data is kept there is a formula which returns "yes" if the students name appears in AS3:AS11 of the Timetable sheet. The index array formula which is not working sits in each cell of my timetable, this finds all records in Classes which match a specific day (say Monday), a specific time (say 09:00) and have "yes" in column S. Taking PHA1 as an example Mak, llektra should be appearing in cells B7:B10 and C13:C14 and B17:B18. Only her BIC2 class appears despite the fact that there is a "yes" in every row for her name in Classes. It may be because I tried to sort the data by student then by class group in Classes...

Can anyone help I desperately need it working by Monday and I'm stumped!

Thank you!!!! I was having a ditzy moment!