You said, " All the online tree showing William B. Mann and Lucy Broadnax as Americus' parents have William dying in 1895 - so this is not likely to be the correct William."
The trees I've seen have Americus V. tacked onto parents who a family that is not his.The William who died in 1895 seems to be another person who was married to another woman - not Lucy Brodnax.There are at least two persons named "William B. Mann", and the one that died in 1895 is the wrong one.
I've contacted Joy McDaniel who may have the Williams sorted out.Here's what got this started:
"Posted by: Raymond L Mann Jr (ID *****7948) Date: February 21, 2012 at 07:46:43 In Reply to: Re: JOHN WESLEY MANN/S.E. GA OR N.E. FLA. by Ed Shipp of 6639
The father of David C. Mann who served in the Wilcox County Rifles was William B. Mann, but not the William B. Mann who married Lucy Broadnax in Hancock County Jan. 1, 1829. Lucy was a widow by 1850 and that William B. Mann was dead. William B. Mann, father of David C. Mann, married first, Jane Payne, and Jane Payne was the mother of all his children. She died about 1846, possibly from childbirth of Elanander Graham Mann. William B. Mann married second, Jane Fountain, April 22, 1846. His third wife was Martha Gunn. The death certificate of William's daughter Elizabeth Jane Mann who died in 1919, shows that her mother's maiden name was Jane Payne. The longstanding confusion of the two persons named William B. Mann was untangled by Joy McDaniel in her posting on genforum.genealogy.com/ga/wilcox and we are indebted to her for the above information.
William B. Mann was born about 1812, son of David Mann who was born between 1780-1783 in Montgomery County, married Peggy Walker in 1809 in Jefferson County and died 1830 in Wilkinson County. The mother of William B. Mann was Peggy Walker. William B. Mann died in 1895. He is buried in the Mann-Harvey Cemetery in Pineview, Georgia. His grandfather was William Mann who was b. about 1760 in North Carolina, served in the Revolutionary War, was granted land along the Altamaha River near where it is formed by the Ocmulgee and Oconee and settled there soon after the area was opened to settlement. He died in Appling County in 1826."