The RRDB is precisely where that list comes from, and because of that, the list has never and will never be completely accurate.
There is also a bit of misinterpretation of the RRDB data going on in that document, as well as some misleading presentation of the data. For example, they have lumped numerous Motorola 3600 (aka Type II) systems that feature P25 CAI talkgroups into the mix. Those are not true P25 systems.
I believe you need to be a premium member to view this report, but here is the list of all P25 trunked systems in the RRDB (may as well go right to the source, right?):
The most complete database of radio communications data
www.radioreference.com
Alternate link if you only want to see Phase II capable systems:
The most complete database of radio communications data
www.radioreference.com