I think it was logical the base it on the existing postal routing zones, and even better to assign a unique code to each and every property. Makes life much easier for couriers and emergency services than the broader area codes in use elsewhere, like in the UK where each code can cover up to 100 properties.
If you put in Killenaule for the address, Tipperary for the County, 2023 for the year, January for the start month and December for the end month.
As a former courier, let me respectfully disagree.
Yeah, there have been multiple cases over the years of ambulances showing up at the wrong location or to late due to difficulty finding rural houses. My parents stopped putting the townland on their business correspondence as post was often misrouted and delayed as there was more than one townland of the same name in the county.
I said "most", not "every".
Certainly not in rural parts...and especially where you can have multiple families with the same first and family names. Our local posties were always great at confirming whether post was for my father or his nephew depending on what the envelope was. And one time I got a postcard correctly delivered to me instead of the other person who shares my name as they knew that I had spent time living in the postcard location!