Why aren't you using standard center codes for regions? For instance ZAU - for Chicago Center (Aurora, IL) when I am looking up preferred routes. I see you are using ZCH.
We weren't using the standard center codes because we were don't intend for all airports covered by a center or approach facility to be considered the metro area of the city named. For example, ZHU will only cover the metro Houston airports even though ZHU controls airspace for hundreds of miles in various directions.
Originally, the cities implemented for FlightAware's metro area searches were Los Angeles & New York and perhaps out of habit, ZNY & ZLA were selected as the terminal area codes, which also set the precedent that we use Z followed by city initials. As you observed, the consistency went downhill and it led to more confusion.
We've switched to the proper center codes (such as ZAU for Chicago) now, but may later choose our own naming system that does not begin with Z if there is confusion about what should be covered or if we decide to launch tracking services that are based on ATC facilities.
We continue to support the aliases NYC, WAS, and CHI for New York, Washington D.C., and Chicago, respectively.
Where are they listed so I know what to type?
They are listed here
Some airplanes also are missing tracklog history after a period of a few days. What is the criteria for it being available if I manually append /tracklog to the tail number link?
Of course, all this stuff is in development and we have some pretty cool plans for both the short term and near term future. Additionally, you've clearly noticed that FlightAware doesn't currently offer to show you the tracklog except when the flight is en route. That said, as it stands now, track logs should be available (via adding /tracklog to the URL) for 48-72 hours after the last flight for that identification arrived. If you've been seeing flights thare landed <48 hours ago with missing track data, I'd be interested in hearing about detailed specifics of the incident. Of course, we still save the data indefinitely, it's just a matter of how far back the map server is willing to look back while it tries to produce a real-time for you.
Thanks for your insightful feedback.