Irish holidays not showing in Mac & iOS Calendar apps?

According to info on the web, a Mac should show the public/bank/some religious holidays in the Calendar app, according to the country chosen in the Language and Region System Preference (and if the Show Holidays Calendar option is ticked in Calendar preferences).

It's never worked on my Macs, since the introduction of the Calendar app (replacing iCal), but it never really bothered me that it didn't work for Ireland, as I just subscribed to the old iCal calendars which are available on Apple's servers (handy, as you can subscribe to multiple holiday calendars, if you work with people in other countries), although they haven't been updated since 2010, and I have now found that they are not populated past Christmas 2018.

I tested the current system, and found that if I change the Region on my Mac to UK, US, or France, the holidays for those countries populate my Calendar app (not that useful though, because even the UK bank holidays are largely different to ours).
As soon as I change the Region setting back to Ireland, there are no holidays shown at all - annoying when you are trying to organise future events, etc.

Does this affect all Irish-region-set Macs, or is my AppleID at fault? (the same thing happens with Irish/other regions on my iPhone).

Note that if you're changing the region, you have to un-tick/re-tick the Show Holidays Calendar in Calendar preferences, to get the Mac to refresh things.