^As a follow-up to my above points, also consider the following:
The events of "The Neutral Zone" and the deadly force that Picard surmised was more powerful than either the Federation or the Romulans. It's likely Picard's hypothesis didn't make sense to anyone at the time it was postulated, but once the Collective was discovered, it became another piece of the Borg puzzle. Bits and pieces of information don't always make sense until they can be linked together to form something more complete. Strange cybernetic beings in and off themselves doesn't necessarily equal the Borg without more information.