Was Forrest the only Admiral? And when he was killed a new "only Admiral" was promoted to that position?
In Broken Bow there was also an Admiral Leonard, and in the episode, as well as the exterior stock shot of Starfleet Command used frequently throughout the series several background extras in Admiral's uniform can be seen.
When Forrest was killed, Archer answered to Admiral Gardner. Interestingly enough, though Gardner is mentioned frequently in the fourth season, the only time he is seen is in fact in the MU. Gardner was also mentioned in season 1, though there he was a Captain, and apparentally Soval's preferred choice to command the NX-01.