Thank you very much for sending your query to Ireland Reaching Out.
Wow you really conducted quite and exhaustive search in Skull when you were there. You checked all the right records. Hopefully we can help find more information with the help of the local community in Glan. Was there another church nearby the townland of Glan? Try contacting the County Library or Heritage Office in Cork to see if graveyard inscription shave been carried out in the vicinity. There might be a much older graveyard which is no longer used in the area. This could have been overlooked.
Best of luck in your research and keep in touch.