Since a 500 GB can expectedly hold 75 HD hrs, it can vary, depending on content, whether its recordings, or Amazon. If you use Netflix, it does not count.
If you have purchased any Amazon video, it would be in your video library, and to get it to you Tivo, you must get it downloaded there from the web site, not from Tivo's Amazon menu. Otherwise, its another purchase.
Series 2 (Retired, sold)
TiVo HD 1TB (157 HD Hrs, PLS, "S3HD")
Roamio, Oh Roamio!
The TiVo Apocalypse begins on Sat 2013 Feb 16 00:00 GMT!