It could be that one (or more) was early term, and didn't get a memorial tattoo, while another was late term and did. I know some women with fertility issues who had several early miscarriages. The sorrow of it meant that they resisted getting excited or attached, picking out names, having baby showers, sending out announcements, and all that jazz, until they were absolutely 100% certain that it was safe to get their hopes up again.