Hanson would have no reason to 'round off' the number of ships he said he was assigning.
He wasn't "assigning" out of a pool, he was gathering
everything he could get, including enemy vessels! He had no clear idea how many would make it in time - he hoped forty would be "just for starters".
The Excelsior-class ship from the beginning, just drops him off and then leaves.
How could she leave? By the time she reaches Earth or Wolf 359, the Borg threat is already well known - failing to participate in the battle would be odd to the extreme.
There's no reason to think that it was his flagship.
...Other than certain other flagships in TNG supposedly being
Excelsiors (we never quite learn what class the
Gorkon in "Descent" ought to be, but backstage books say she's another of that class), and the red alert graphic indeed harkening back to the days when Starfleet built
Excelsiors.
Why do we count an assimilated crew member as a "survivor"? Anyway, no doubt hundreds at least were assimilated in the battle: the Borg like to do boarding, and if they managed to get
one assimilated Fed from Wolf to the Delta Quadrant, this probably means they assimilated a ship for the purpose and plenty of other people along with it...
But speculation is speculation. The only "clear-cut" things regarding the battle are the survival of the two Siskos, the perishing of 39 ships (only four with known names -
Tolstoy,
Kyushu,
Melbourne,
Saratoga) and 11,000 people (only one known name, Hanson, although that VOY "Survival Instinct" assimilee was probably counted among the 11,000 rather than separately listed in some other category), and that's it. No information whatsoever of other surviving ships or personnel, except in speculation.
Was there ever any explanation given why the civilians on-board Sisko's ship weren't evacuated before he engaged the Borg? Were they pressed for time?
Nothing given, but it's easy to see Ben Sisko knows what he is facing from the first close-up in "Emissary" already. It's a decisive fight for the entire human civilization; if Ben fails and dies, it's probably much better for Jen and Jake to die as well than to be subjected to the horrors of surviving. At least a starship offers reasonable chances of committing suicide if assimilation looms... Somebody will remain unassimilated long enough to kill the others with a push of a button, a maneuver less likely to work on some colony or homeworld.
Timo Saloniemi