Glasgow-boy:
Alert: I've not seen the answer in the mess that is the Regulations, old, new, or still in gestation.
That said, I've done license conversions before for two other regulators and converted my own license to the CASA system. I have an invalid UK-issued license right now, actually.
For license conversion,
a license is invalid, defunct, to-be-ignored, unless it is current and accompanied by an appropriate & current medical.
In this context, "current" means AFR or BFR not expired, at least one valid class rating, competency checks or renewals completed, and privileges able to be exercised legally right now in the home country.
Sorry for the wordiness. But I personally used to hear all the arguments as to why the rules didn't
really apply to the chap in front of me. (Made some of them myself, once or twice.
)
Never did manage to convince a regulatory bureaucrat though!