Tinstaafl,
Many thanks for taking the time to respond and for an explanation which makes it all crystal clear. I can't believe (and I'm embarrassed to admit!) that I've sat in a classroom for three months and failed to pick up on these points. I'm a borderline case on Met, but here's hoping I've now secured another mark or two.
You must be an Instructor (and if you're not, you should be!)
Thanks again! Hope I can reciprocate sometime.