This article implies there are approximately 6 million more first mortgages than the last US stated (warning big PDF).
Because credit cards are more common than mortgages — 51.4 million households have first mortgages, while nearly all the nation's 114 million households have at least one card — card-related actions can hurt overall scores more than mortgages.
If the non-governmental number is correct it puts more properties in jeopardy for potential problems. Although even properties that do not have mortgage can still run into tax problems or other types of liens. Here is the list for mortgage characteristics from the last American Housing Survey -
And also notice the 13,966,000 homeowners that have HELs or HELOCs. This reporting is dependent on them actually realizing the money, that they believe is theirs, is actually equity. We have seen in a previous post that there is a sub group of the population that does not realize spending on equity credit cards is using their equity.