Diffrence between 2 VCF files

Question

[khatami.mahshid]

Hi all,

I found VCF file for Denisova in UCSC genome browser in this link. but there is a paragraph in explanation of UCSC that introduce a new link for Denisova, this is the link. the paragraph is this:

Comprehensive VCF files that include information for homozygous-reference bases and uncovered bases are available. This track uses VCF files that were filtered to retain only those locations that clearly differ from the human reference genome. Reference genome bases without variant calls may indicate either matching Denisova sequence or insufficient data.

I couldn't understand the difference between these 2 VCF files database. can anybody help me with this?

thanks a lot