Pretty sure Cayce did not fake it. Cayce in his conscious state had absolutely no interest in these matters. You have to dig into his personality to understand, being a devout believer in the Bible, atlanteans hiding records would apear like complete fiction. But the information he passed when in trance was indeed shocking. His version is that the Sphinx indeed connects to other pyramids, but they are located to the south, between the Spinx and the river. These pyramids have not been located yet, so the records are stil hidden.
Around the date Doreal supposedly found the Thoth records, the Rosicrucians also claimed the location of a temple and drawings of such can be found in Randall-Stevens and another writer which becomes confusing even because one or the other copied...lol. Anyway the topic seemed to be trendy even then.