I vastly agree with this from @Edent about names and special characters.
We can throw Welsh names into the misspellings required – Siôn, Siân, Glyndŵr, to name a few.
I think these 'unusual characters' just aren't on this list. It's where this journey started in the sixties and its vestiges live on.
My mom also almost got rejected at the US border once because her name starts with 'Þ' and it's like that on her passport, but since we couldn't use that letter on the plane ticket we used 'Th' instead and the border agent found it suspicious
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