Blanks mean there is not a recorded loan. Could be a private loan or paid off property.
It means that the supporting information is lacking, thus we may be lacking the "Original Loan Amount" or we may not have been provided a "Current AVM" (Automated Valuation Model) to know the value of the home at this time.
It could also mean that the home is paid off, although this is not often the case unless it's an older area.
We currently have no way to know how many cumulative payments they have made. So it's only based on original loan amount and current estimated sale price.
It's just a simple two factor division of Original Loan Amount / Current Estimated Value
If the person has an interest only loan or some other financial situation, like they took out an HELOC, it will not be represented in that number.
Also LTV does not mean equity in the home. That just means remaining loan outstanding. It does not take into consideration the current market value of the home.