That piece of information is included, albeit not explicitly stated, in the above and in this quote, "If the PCs are in different rooms, use separate powerline adapters."
Explicitly stated, you can use multiple powerline adapters in the same home.
The total throughput is limited by the technology of the set and shared among all adapters in use. In practice, the results are unpredictable but recent technologies should be acceptable for most uses. While I no longer use powerline on my networks, the common recommendation around here is AV2-1200 as a minimum. Always buy from a seller with a customer friendly return policy incase the set doesn't work for you. I live in a major city with several large stores nearby. My personal...