Reported by Stuff,
Collingwood headstone mystery solved and family found on Wikitree
...tombstone remains once marked the grave of seafarer Christopher McGarry who was buried out at the North Head of Westhaven (Whanganui) Inlet in mid-1866.
In this case, it took my book to get published for Sally Gaffney, a research archivist at the Golden Bay Museum to get in touch with details supplied by museum veteran Penny Griffith, who forwarded a net-published wikitree entry.
https://www.stuff.co.nz/nelson-mail/300837878/tombstone-mystery-sorted