I’ve moved your post back into the thread you already created. It’s best to keep information on the same people in one place.
As you already know Denis’s parents are Richard Lynch and Margaret Dennehy, I think you can be confident that the birth you found is right: 11/3/1879.
The corresponding baptism is 9/3/1879 in Inishannon parish https://registers.nli.ie/pages/vtls000634133_128
The slight discrepancy in the dates is probably just inaccuracy – but he could not have been born on 11th if he was baptised on 9th.