A lot of nuance here for certain aspects. 

RTK can be obtained by the farmer or user's own base station(s) and rover setup. It can be from cellular systems. It can be from satellite systems. Even from the same brand or manufacturer. 

Boundaries or anything (guidance lines) can "move" just from one base station to another depending on how, and how well they were surveyed when installed. Jim could have one base station and Mike another base station that's exactly the same brand/model and they live next to each other. If they weren't BOTH surveyed well or the same, if you switched  from using one base station to the other it could be different. Same field, same spot, same machine. This goes for any brand, and even within brand. 

Cell can vary from base stations. Satellite can vary from cell and base stations. Etc etc. Again, even within brands let alone across brands. So RTK is precise, but when you start crossing signal sources and brands it may not be as accurate or reliable. 

"RTK" does not mean any brand with any GPS source can pull into a boundary and it all magically aligns. Some brands and signals know if one is offset from another and can provide those so things can be adjusted. Once the public free CORS networks in IA, MN, OH, and others move to the new Datum things will get even more funky for a while for people using those.