LastSystemUpTimePollUTC not updating for WMI node

I have a custom query that lists devices that are not currently polling by SNMP or WMI for statistics. The query uses the LastSystemUpTimePollUTC timestamp from the NodesStatistics table. However, a spot check reveals a few devices that will successfully poll for WMI. I look in the database for that node and can see that the value for the LastSystemUpTimePollUTC is indeed about 3 months old. How is this happening? Why is the value not updating? Thoughts?