Same serial numbers but different years
I am new to collecting coins as well as currency. I was looking on ebay this morning and I found a $1 bill that had the exact serial number as my $1 bill. I know that it wouldn't be possible in the same year/series. They have Different years and series, my question is, how common is that? And the serial numbers are 72777777. Sorry I'm also new to this forum, I suppose this doesn't go in the us coin forum..