Violet-green Swallows checking nestbox

Today (4-14-14) the female Violet-green Swallow is repeatedly entering the nestbox, apparently planning to use it for nesting this year.  Every year when I watch this I wonder if it is the same female from a previous year, one of the young birds that hatched in this box, or a newcomer.  But I tend to think it is a bird who has been here before, judging by her seemingly instant familiarity with the neighborhood and the location of the nestbox.