While I have written about reported birthdates ranging over several years, something else that happens from time to time is the reporting of death dates, especially gravestones, being off by a few years. Sometimes, when a gravestone date is off, it also creates an incorrect birthdate.
This example involves Joel Chafee (usually spelled Chaffee) of Thompson, Connecticut. He is buried at Wilsonville Cemetery in Thompson and apparently has two gravestones, one that has fallen down and one that still stands erect. Both stones state essentially the same information, that he died 5 December 1863, aged 67 years, 2 months, and 9 days. As a consequence of this age on his stone, his findagrave entry currently credits him with a calculated birth of 28 September 1796. He is buried beside his wife Lavine (Morse) Chafee, who died in the same year, on 2 June. From her age on the stone, it would appear Joel and Lavine are the same age.
I next tried to verify these events from vital records. I found Lavine’s death in Oxford, Massachusetts (two towns north of Thompson), with the date of death and age at death as given on the tombstone. However, this death record referred to her as widowed! If Joel had died in December 1863, Lavine should still have been married. Joel and Lavine appear together in the 1850 census in Thompson, but she appears in the 1860 census in Worcester, Massachusetts, with her married daughter and without Joel. In the 1850 census, Joel is aged 63, which would be more consistent with a birth in 1786 or 1787, rather than his “calculated” birth year of 1796. Turning to Thompson Vital Records, I find Joel Chaffee, son of Thomas and Mary, born on 27 September 1785.
My immediate thought was that the date on Joel’s gravestone was off by ten years and that he died in 1853. If you calculate the age on his tombstone and substitute 1863 for 1853, then this is roughly the birthdate found above in the vital records (within a year). Further confirming this, Joel’s probate was administered 8 April 1854, and, finally, his death notice appears in the Hartford Courant with the date of 5 December 1853 and the report that he died in nearby Pomfret. (This death was not found in the Pomfret or Thompson vital records.)
I suppose no grave was erected for the dates between Joel’s death and that of his wife, and perhaps the stone cutter made a mistake and assumed the couple had died in the same year, following all the other instructions accordingly.
For some of our ancestors in the nineteenth century, a gravestone may be our only source for a death date. When possible, try to confirm that the year makes sense and is not off by a few (or ten!) years.
 Massachusetts Vital Records, Deaths, 1863, 167: 261.
 Thompson Vital Records, 1: 17.
 Connecticut Probate Records, Thompson Probate District, Joel Chaffee, Thompson, 1854, No. 270.