I dont know the source of this index that Find My Past have, but maybe there's a typo or mistake in the index, or the notice actually in a different paper ?
The dates tally, which is strange... I dont think there were two different editions of the paper, and it doesn't sound like a late notification as it's two days later.
Did you find the section for the death notices ok in the papers you looked at ?
Usually these were at the top left of page 1, but sometimes were continued on another page if these overran.
Have you asked Mount Jerome do do a search for you in their registers ?
After Glasnevin I think this is most likely location. There is a charge for a search .. might be the only way to confirm or rule out Mount Jerome, particularly if there isn't a headstone..
S.