Q and some A s

When its it appropriate to hold another referendum on the same subject ? When you lost the  first one.(If you won it, it is settled for a generation.)

If the UK votes to stay in the EU will the Scots mind if we have another referendum a few years later?

Why is it ok for Scotland to have a referendum on seceding from a country it has been part of for hundreds of years but not ok for the UK to have a referendum on seceding from a non country it has only been a member of for 40 years and has caused it nothing but grief?