Now you're getting technical mutt!
Validation - can't be accepted by other states (1.015b). It is only valid for that 'state' registered aircraft. You can't transfer a validation.
Conversion issued on the basis of agreement between two regulators (FAA/CAA) - doesn't have to be accepted by other states (1.015c)
Conversion issued by being given credit for previous experience and licences - is accepted by other states (1.016)
My personal grievance (and plenty more others) is the insistance by the CAA that experienced single-pilot IFR drivers are required to complete a 50 hour IF course. CAA have the ability to 'reduce the course duration, number of lessons and specific training' under 1.016 which they do for the issue of a CPL but refuse to do for an IR. Some people call it protectionist - I call it plain and simple stupidity!