I don't believe that I have any "memory full" problems with my guide as speculated some might have.
So my guide does update as I am in it, like Whidbey described. (on all firmware versions)
If a channel is showing "no information" in the guide even after just doing a guide download at power on,
when I choose it in the guide and then move to another channel in the guide, the missing info fills.
I have had occasions when the guide info doesn't fill as desribed, but those were station PSIP problems confirmed on other tuners.
You could also loose guide data at six days out, that was originally in the box when a station lessens the amount of guide data they are sending.
The stations are in control of most aspects of the guide info.