Yeah - great point. I'm actually working on a way to detect if a set of IDs are being used on the same workbook. This is possible technically via some environment variables inherent to the spreadsheet - but it opens up another can of worms on the privacy side of information I'd have to collect.

I think the short-term solution will be to throttle unique ID creation to 5 / email - not perfect, but I'm a one-man team so will have to bite at this problem step-wise :)