Rereading the Ringworld books, it occurred to me to question the timeline. In particular, the Ringworld has a series of full-size populated maps of planets of other species' worlds, which are speculated to be a way for the Pak to monitor and experiment with those species. One is of Earth.
Earth was a colonization failure for the Pak; tree-of-life would grow, but the microbes for the transformation were missing. After thousands or millions of years, it was rediscovered by Phssthpok in archival records, and he came to set things right. IIRC, he arrived around 2100AD, meeting an asteroid miner Jack Brennan who, after transforming into a protector himself, killed Phssthpok. It's possible he got a message off to his Pak buddies before dying, but it would have traveled at the speed of light, as the Pak had no superluminal capability.
Ringworld appears to take place around the late 2900s:
The Arch seemed to blaze above them. A thousand miles above the Ringworld, they could see how the Arch merged into the rim walls and the flat landscape. Like the first man in space, a thousand years ago, looking down on an Earth that, by Jahweh and his mighty hammer, really was round.
Guessing about 900 years between Phssthpok's discovery and Louis Wu's first trip to the Ringworld...which has been Pak-abandoned for at least 100,000 years by the most conservative estimate of genetic drift...why do they have a detailed map of Earth built into it when Earth was rediscovered only 900 years earlier? Before that, they thought of Earth as populated, if at all, by subsentient breeders. Phssthpok himself was astounded to meet a breeder he could talk to, so the state of Earth couldn't have been common knowledge when the Ringworld was built.