Don't know if others are experiencing this and if it's TBE (To Be Expected), but when the guide data refreshes (about 9AM local time each day) I look at the DVR log and have noticed the following behaviour.
21 day (504hr) guide, being refreshed in 6 hr blocks
A 6-7 day black-hole from day 11-17or18 (no guide data retreived)
Each daily refresh gets;
10.25 day guide data (246 hrs) hours 1-246
6.25 day black-hole (150 hrs) hours 247-396
1 day guide data (24 hrs) hours 397-420
3 day black-hole (84 hrs) hours 421-504
and last 6 of 21 days in web ui guide from 6pm-9pm (prime time) are usually blank
zap2it.com has guide listings for 14 days, I'm not sure what part of the Channels 21 day guide we're getting beyond the first 10 days? I'm sure there's a reason for why it does what is does, but I don't know the reason.
I realize that a lot can change in 21 days, so maybe this was all thought out before I even started using Channels?