That is what I was saying. From wheel to tread, OEM 18 inch has more sidewall than 20. Never said anything about wall thickness. Load rating goes with the type of tier you use and the load index.
If they are OEM, they should learn automatically. The only thing I don't know is if they have changed the frequency set for the OEM TPMS lately. Though I doubt they have.
Regardless of cost, I always buy new OEM TPMS valves if I purchase new wheels. A lot of times, at least one of the removed valves will get damaged during removal and need to be replaced.
If you have a Windows computer and a CD drive, you can use Windows Medeia player to rip them to MP3. I haven't done it in awhile but it had some decent settings for gain and bit rates when I used it pre Windows 10.