Silly Question - If there were alleged sightings in 1552 and 1592, how come Sebald de Weerdt's sighting is undisputed ?

To be pedantic the vote on the Good Friday Agreement was not strictly speaking an All-Ireland vote, because the questions asked North and South were very different. However both referenda endorsed the Good Friday Agreement which recognises the de facto constitutional position that Northern Ireland is (administered as) part of the United Kingdom.

And while we're on matters constitutional, the name of the 26 county country according to Bunreacht na hEireann (the Irish constitution) when speaking the English Language is Ireland. In the first official language the name of the country is Eire, but that's not the langauge spoken by most people around here. Ireland was declared a Republic in 1948/9 but its name didn't change. Republic of Ireland refers to its football (Soccer) team only.

The official name of the 6 county state is Northern Ireland. The reference to Ulster goes back to the day's when some people were hoping to keep all 9 counties in the UK, but that didn't happen. Neither did the boundary commission.