Therefore, my advice to you is that, even if you think you've gathered all the definitive information for one location, always check other similar sources if you happen across them. Read on for the tale of Henry Revell to illustrate my point.
My cousin, Jackie had shared her own original research with me and I also photographed the graves myself in 2016 - you should be able to just about make out Henry's name in this photo, roughly in the middle of the inscription. However, many of the gravestones had already taken a battering from the "soft" Irish weather, so I decided to try some further sources to learn more.
The Representative Church Body Library (RCBL) in Dublin had the original parish registers [1783-1858] from which I painstakingly transcribed out all the relevant burials I could find, including a Henry Revell buried in 1840. This was in all likelihood this man (his mother Jane inscribed before him was buried in 1837 and the John inscribed below him was buried in 1842.) The RCBL also had an unique source in the form of a plan of the churchyard made in 1908 by Stanley Lane-Poole. Stanley also published some extracts of this plan in the Journal of the Association for the Preservation of the Memorials of the Dead in 1909. Some Revell graves were mentioned, but not this one with Henry Revell? Stanley also pointed out in his introduction that there were significant gaps in the early burial register compared to his plan, which proved to be sage advice when trying to track down other Revell burials that should have been there!
Who else might help - Brian Cantwell of course! Brian had done some wonderful transcriptions of many Wicklow headstones in the last 20 years of his life before his death in 1992. These can be found in printed form in many Irish libraries and archives and are also available, indexed, online with FindMyPast. But curiously, Henry was not recorded as an occupant of this grave, yet all the other occupants were? This must have been a transcription error on Brian's part surely as Henry's name was clearly visible to me in 2016?
Joyce Tunstead had also taken some excellent photos of Dunganstown headstones in 2009 and published them on IGP but curiously there were NO Revell inscriptions recorded at all? Again, given the evidence of my own photo in 2016, this slab was clearly visible along with its Revell neighbour - why did Joyce not include it I wonder? Other flat slabs nearby were included, just not these ones?
So, in 3 of these sources there was nothing for Henry Revell. By taking a photograph myself and corroborating via the burial registers, I could eventually confirm his demise, but I was left perplexed as to why several other people had left him, and other Revells, out of their gravestone research.
Therefore, never pass up the opportunity to check an alternative source for something you think you already know as you may find more than you're looking for.