Were they named MERCY or MARCY?

Seems there is a great deal of confusion over the spelling of this female name in my Wheeler and Watson family lines in the 18^th and early 19^th centuries.

The mother of my ancestor, Desire Wheeler Watson, I thought was Mercy Williams who married Thomas Wheeler. Here is an excerpt from the American Genealogist, vole 82, 2007 pages 60-61 as shown on the NEHGS website:  

A look at the family of Mercy Wheeler, first wife of Capt. Christoper Gardner of South Kingstown, provides additional argument that Rufus Gardener of New London was likely their son.  She is presented in The Gardiners of Narragansett as “a daughter of Thomas and Mercy (Williams) Wheeler.” ……In his will of 28 November 1760, proved on 6 January 1761, Thomas Wheeler of Stonington. “in a Weak and Low Status of Body”, names his wife, Marcy, son Thomas …. Daughter Marcy Gardner ….There is no estate file for Thomas’s widow, Mercy, in Stonington.

Well, which is it ?? Seems to change back and forth between using E or A, as I have seen with others, including these two who confused me when I first found the name spelled with an A.

       Mercy Watson 1778-1817, wife of Ezra Lester

       Mercy Watson 1810-1882, wife of Col John Watson

           Her NYC death certificate & Woodlawn memorial both use A

           Seems she was named for her aunt Mrs Mercy Lester above

Today I found another one, Mercy Stanton …or was it Marcy? Looks like A wins in this case.

Albany land record from 1830 as displayed on AmericanAncestors.org:

Grantor: Rufus, wife Marcy, et al. WATSON

However, Google Books displayed some biographical info as follows:

        Rufus, son of John and Desire (Wheeler) Watson, was born 1774; died 1856; married MERCY Stanton, born May 22, 1784

Plus an excerpt from the local agricultural journal listing MARCY Watson as winning accolades for her spinning (The Plough Boy, vol 2, p163)

Her 1836 death was reported in the Newport (RI) Mercury as  Mrs MARCY Watson, wife of Rufus and daughter of Benjamin Stanton.

So, I guess I’ll assume the pronunciation perhaps caused the spelling variations. At least I do feel more assured that it is the same person regardless of the vowel.