On the other hand the only rationale for 3 planets seems to be the amount of scans from this site. (I haven't seen any other rationale but obviously could have missed something, so please correct me if I'm wrong

)
Other info we have would suggest more sites:
- 3 Arks (H12)
- Subsequent hyperspace technology and expansion into the galaxy (H13)
- An interstellar comms network H13&14
- The network(s) is(are) arranged in geometrical patterns (C12) (The sentence in question mixes up singular and plural)
I realise this is a semantic/linguistic arguement on the last two points, but I don't think a single triangle can really be described as a pattern. For the network to be described as being in a geometrical pattern, I think that you'd really need several triangles arranged in, well for want of a better word, a pattern

.
I can't see anything specifically stating that the ruins is part of the network so it is just conjecture, but it seems reasonable to me to assume that it would have been.
All in all, I would say things tend to indicate more than 2 other sites.