Ann: Trading Halt, page-79

A theory that makes very good sense.

Big contracts take time for both parties to sign (damm lawyers ). The bigger the contract the more sensitive either party can be to any announcement before it's official. It isn't official until all signatures are on the contract. I have seen an instance where the senior party pulled out of a contract because the other advertised that they had the contract before it was signed.
An example is where the principal wants to notify the other tenderers that they were unsuccessful before public notice of the successful tender.