There is an implied priority in your formula - it will try to find a
match in the Oasis Pemb sheet first,and if there is a match it will
eturn values from there (ignoring the Oasis Minor sheet). If it doesn't
find a match in Oasis Pemb then it will look in Oasis Minor. So, in
order to get it to retrieve values from Oasis Minor, you must ensure
that there is no match in the other sheet.

By the way, you have a mixture of relative and absolute addresses for
the ranges - I would suggest making them all absolute to avoid any
confusion.

Hope this helps.

Pete