"The TiVo Slide Pro, Glo Premium, and Slide remotes are learning remotes, which means they can learn certain functions from other remote control devices without requiring a device code."
which I took to mean that there were Glo remotes and Glo Premium remotes produced.
Further assisting me in this apparent misconception,
Press and hold the TiVo and Select buttons simultaneously for 3 seconds. When the red or amber activity light remains lit, the remote is in "learning mode."
and on the three of these remotes I wound up with because they came along with used TiVos I acquired, on only one of them does holding down both of those buttons lead to the red light coming on and staying lit.
Maybe I just wasn't "im-press-ive" enough on the first two.