The possibilities range from a name change/borrowing a name to
half-brothers or cousins to just a regular mistake.
One of my relatives had five sons, two of whom used variations of their
names (Israel/Isadore, Jack/Jake) during their lifetimes. I have seen
versions of the tree that show seven sons -- unrelated men with those
duplicate names have been grafted on to the tree. I was initially kind
of confused, but because the brothers were born in Chicago around 1900,
I could find actual census records and sort it out.
JoAnne Goldberg - Menlo Park, California; GEDmatch M131535
BLOCH, SEGAL, FRIDMAN, KAMINSKY, PLOTNIK/KIN -- LIthuania
GOLDSCHMIDT, HAMMERSCHLAG,HEILBRUNN, REIS(S), EDELMUTH, ROTHSCHILD, SPEI(Y)ER -- Hesse, Germany
COHEN, KAMP, HARFF, FLECK, FRÖHLICH, HAUSMANN, DANIEL -- Rhineland, Germany