G'Day again
This is another headstone inscription from Bangor Abbey that covers my family. As you can see on the headstone that Henry Montgomery was married once before he married Agnes Harper. Of course you are right about the will extract being the right date of death as you found the birth of Jane Montgomery born April 1864.
Regards David
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Transcription of headstone: "Erected in memory of the late John Montgomery of Bangor. who departed this life 16th February 1841 aged 81 years. Also of Margaret Montgomery, wife of his son Henry Montgomery of Belfast, who departed this life 1st of May 1842 aged 26 years. The Lord was ready to save me Isaiah XXXVIII, 20. Also of Eleanor Montgomery, daughter of Hugh Montgomery, who departed this life 24th Sept 1849 aged 2 years. Also of William Montgomery of Belfast, son of John, who departed this life 3rd October 1849 aged 40 years. Also of Agnes, wife of Hugh, who departed this life 14th Dec 1849 aged 37 years. Also of the above Hugh Montgomery, son of John, who departed this life 22nd Decr. 1849 aged 42 years. Precious in the sight of the Lord is the death of his Saints Ps CXVI, 15. Blessed are the dead which die in the Lord Rev XIV.13. Also his wife Mary Montgomery, who departed [blank] February 1859 aged 84 years."