Dual Grounding Electrodes In Parallel versus series
I can't find anything that says you can't have it the way that you do. As long as each physical service has at least one ground of its own I think you're fine. Isolated ground systems aren't uncommon these days in residential dwellings, and that's how you'd do it (except you'd shield it and land it to an isolated ground bar in the can).
I've built large ground rings to deal with lightning which were always in series (#2 tin coat copper Cad Welded to 6 - 8 rods together about 10' apart, depending on the soil), but that was because we had to get extremely low resistance. The service grounds were completely separate. These are mandatory at cellular tower sites.
So with your setup, you just have options. Ever get any equipment that is particularly sensitive to noise? It would not be hard to set up an isolated ground bar and some IG receptacles. Or, just have fun measuring :)