Thanks Jay!

I should have made it more clear that I don't want to count each instance
of, for example, code 1, whether it appeared as a 1 or as included in code 5,
only unique values.

However, I managed to use a formula to count cells where I'd already broken
the codes down into the subjects they represented, so I have the result I was
looking for after all.

Thank you for your help, anyway. :)

Formulae I can manage, but trying to get my head clear on functions, nesting
functions, making sure all the arguments are included (and how they can be
part of arguments for other nested functions) and that I haven't forgotten a
bracket somewhere - phew! Head spinning!!