We have to assume that the plaintiffs are aware of that basic fact of copyright law and have some argument, however thin, that what was taken is their original expression of that time zone history.
In Feist (the phone book case), for example, the plaintiffs never claimed that they owned the phone number facts. They claimed that they owned the expression of the phone numbers as a single compilation in alphabetical order. The court found that that particular expression was not sufficiently original to be protected by copyright.
It seems to be a mistake on the astrologers' part that they published their findings. They should have sold them under NDA to people willing to pay for them. There must be more to it, like that they originally didn't think the research itself was very valuable and have changed their minds.
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