I think the closest you will come is to go to your TiVo account and click on billing history. There you can look at your Tivos (one at a time, unfortunately) and see which ones you paid "full price" for.
I don't know how accurate it is, though. I have 3 Tivos, an S2 and two TivoHDs.
My first Tivo was the S2, paid full price lifetime. I got both TivoHD lifetimes with the MSD.
However online, TiVo shows one of my TivoHDs as having the full price sub when it should be on the S2.