Why does "Patch ..." sometimes miss updates?

[coover]

Right now, there are updates available for KC Software's SUMo and Crystal Disk Info. SUMO has been available for several days and CDI for, probably 24 hours, at least, but Patch My PC does not see those updates or install those updates even when manually requested.

I do not know how the software knows when updates are available, but, at least with these two, it seems like it is taking too long for it to happen.