Ireland: the series starts in 1922, and it is a new index rather than a continuation
Ireland's first official consumer price index was compiled for March 1922, weighted from a household budget inquiry that June in which just 308 households returned usable figures. It kept the base of the index that preceded it, July 1914 = 100, which makes it look like a continuation of the British cost-of-living series covering Ireland before independence. It is not. New weights, new price collection, a new compiler; the numbers happen to share an anchor.
That matters if you are converting from before 1922. The pre-independence figures belong to a different index, and this page does not chain them.
One more limitation on old Irish figures: the index was compiled quarterly until 1976, measured in the middle of February, May, August and November. An annual average from 1950 rests on four observations, not twelve, so treat a single year's conversion as approximate rather than precise.
The punt is the one euro conversion that makes the number bigger
Ireland adopted the euro on 1 January 2002 at a fixed rate of 0.787564 punts to the euro. Of the currencies that joined, the punt was the only one worth more than the euro, so a punt price converts upward: a IEP 100 figure is about EUR 127.
People routinely get this backwards, because every other euro-area conversion runs the other way, and because the mental habit from lira, pesetas or francs is to divide by a large number. The index handles the changeover on its own; the trap is in what you type into the box.
Mortgage interest is in this index and out of the European one
Ireland publishes a national CPI and an EU-harmonised HICP. The methods are now identical and the difference is coverage: the HICP leaves out mortgage interest, motor tax and insurance, dwelling and contents insurance and local property tax, currently around 4.6% of the national index's expenditure weight.
Mortgage interest entered the Irish CPI at the November 1975 rebase, on a user-cost view of owner-occupied housing, and it is in the series used here. During a period of moving interest rates the two measures separate noticeably, so check which one a quoted Irish inflation figure refers to before comparing it with this page.