Historical Typos...

Even history books have typos...well, I'm assuming it was a mistake.
Today's adventure started while I was in the midst of typing out on my computer a local history book by Lucius Marsh, who wrote the book on a typewriter in the late fifties but never had it copyrighted or printed and so all the copys that exist are just photocopies that are three hole punched and put in binders. Worse, he organized his history by location, as in, he thoroughly covered the individual history of each house in Douglas. The histories are then organized by location along the street they are on, then the streets are organized in the book alphabetically. Needless to say, if you need information about a person's life, you have to know all their street addresses. Actually, just the location, since there weren't street numbers.
Therefore, I have undertaken the great task of typing it out on my computer so that it can later be provided as an electronic resource rather than a fat three ring binder and one can just hit Ctrl+F to search for a persons name, or event, or object, such as "axe-shop", as the axe making industry was very influential in the town of Douglas.
However, today as I was going through the book I noticed that it stated that Paul Dudley, an ancestor of mine, was born in 1776 and died in 1857. Which is rediculous, since Paul Dudley was in the Revolutionary War, and I'm quite sure he didn't fight off the Red-Coats as an infant. Also, we have documents that show his widow was recieving money from the Government from Paul's involvment in the Revolution in 1843. If Paul died in 1857, why was his wife a widow in 1843?
After being utterly frustrated with Lucius Marsh, I checked his source, which was Emerson's History of Douglas, published 1879. I found that Marsh did not make the mistake, Emerson did! Emerson's book shows the Paul Dudley died in 1857 at the age of 80 (hence born in 1776ish considering he died in February and was born in August). This same history book records that Paul's first son David was born in 1788. Emerson either actually thought that a man from the colonial era married and had his first son at the age of 12 or didn't look over his work.
Frustrated with both sources, my mother went online and found his marriage was in 1782 (if we beleive Emerson, that would have been when Paul was 6 years old) and confirmed that he was a Private in the Revolutionary War. But, alas, no record of his birthdate.
So, out to the cemetery we went! My mother and I went a few hundred feet out of the house to the Douglas Center Cemetery, found Paul Dudley's grave, and found that he died in 1837 (notice that's just one digit off the earlier number) at the age of 80. With this new date, it means Paul was born in 1756. Therefore, he fought in the Revolutionary War in his 20's, was married at the age of 26, had his first child at the age of 32. Which sounds a lot better.
Message: always check for typos, always check your sources, and if you want to be sure to be accurate, check your sources for typos. Or better yet, just use common sense to figure out if you've made a mistake. Everyone makes mistakes, including reputable historians. I would love to be able to inform Emerson and Marsh of their mistakes, except they're dead.