How many sources do you need to "prove" a statement? There's not a hard and fast answer to this question. It actually depends upon what sources are being used and where those sources got their information. Ten different family histories that make the same statement based upon an earlier family history do not count as 11 sources, they count as one.
Let's say those sources indicate a Revolutionary War veteran died in 1831. His widow's pension application indicates he died in 1837. While there are always exceptions, this case would likely be one where the one source outweighs all the others. The widow's pension application is more likely to be correct than family histories published several lifetimes later.