We are led to believe in the 15 December, 1966 Star Trek episode Balance of Terror, the Federation have not seen a Romulan ship in more than a century. The Enterprise crew goes on to say they have never seen a Romulan. When Uhura finally gets a visual on the Romulan bridge, every Star Fleet member is shocked to see a Vulcan look alike. Lt. Stiles is even racist throughout the whole episode towards Spock.
https://memory-alpha.fandom.com/wiki/Ba ... r_(episode)

Now fast forward to the Enterprise series.
Administrator V'Las has been revealed to be involved with the reunification of the Vulcans and Romulans. So knowing this, it would be assumed that the Vulcans knew who the Romulans were. So why doesn't Star Fleet know about the Romulans, specifically what they look like?
https://memory-alpha.fandom.com/wiki/Unification

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Jega Grant
<#577>
The 12th Fleet
5 year veteran
Engineering Division
"CRY HAVOC....and let slip the dogs of War!"
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Jega I have a theory. First and foremost, the Vulcans were not forthcoming with information during the Enterprise era, they did not trust humans. Second, they wanted to hide any fact that they are related to Romulans. They were able to bury any information on this so, this could lead the TOS era crews to genuinely not know what Romulans looked like.

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Sarah N. Lasker
VA Engineering

Correction: the Enterprise crew did not know what Romulans looked like.

I would postulate that some parts of Starfleet does know what they look like. Serving officers would have no reason to know this classified information.

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