Yes, the apostrophe has a rich history.
Its graphic is strictly upright.
Its two immediate cousins (acute & grave) are a tad more tiddly!
Normally used as diacritics (meant to be written as modifiers above underlying characters) they can also appear as separate characters in their own right.
Particularly so as outputs in transcribed texts.
Especially in computer-graphic-scanned/automatically-"interpreted" productions.
Check out Unicode.org, or NOT!
The standards evolved with the years, and implementations (e.g. ISO character tables) varied across computing platforms (Apple, Microsoft, DEC, IBM, BELL "UNIX"...), creating a huge cross-industry reconciliation problem of the versions levels.
[I worked alongside international language experts at Rank Xerox International once.
Mind blowing stuff.]
The Republic within Ireland banned the use of the "grave" diacritic within Irish Gaelic in 1948.
[No doubt inspired by the rationalisations of the "English" language effected much earlier in the USA.]
I recall chasing a "M'" record once (which I "knew" must be in the online record) to no avail.
Then I put on my "alternative thinking" cap, and tried the "grave" character.
Top left of the keyboard. Bingo!
[Simpler method nowadays, supported by most browser searches, just use a "?" or two, or "*".]
I used to tease my erstwhile old mate, Mr. McHale, that he couldn't take the Mick out of me.
[I'm descended from an O'Hale!]
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Alternative record resource is the Tenison GROVES archive at PRONI.
He was a Record Agent (sort of legal secretary) based in Belfast.
He travelled to Dublin and transcribed many relevant records relating to folks in the North.
His productions are held/indexed (transcribed?) by PRONI.
They are also available on LDS microfilms.
A few are typewritten, but many are in awkward-to-interpret scriptive writing.
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Interesting to see your links with the Channel Islands.
Then, as now, 'Twas a lovely place to live, and also a tax haven!
Ideal place for pensioners (annuitants) to retire.
['Tis why major manufacturers, with links to the continent (e.g KEILLER marmalade, of Dundee), migrated their operations to there. Superb hub from which to access the furthest reaches of "The Empire".]
We had DIGMAN mariners/victuallers in St. Peter Port on Guernsey till around 1865.
Don't know why they went there.
[Though I did find two records of ships sailing direct from Guernsey landing cider at Belfast in the 1790s.]
Pip pip!
Capt Jock