That all does make sense then - the squadron's equipment isn't
that obsolete for 1939, and the A6M would indeed have been top-of-the-line at the time. As for Anabuki, it would be completely normal for her to be flying a Ki-27, since the Ki-43 didn't arrive until 1941. Even Beurling wouldn't have too much to complain about; plenty of RAF units were equipped with Hurricanes well into 1940-41.
They've clearly done their homework thoroughly on dates and equipment. Hats off to the writers and staff.
It's interesting, though, that the novel seems to imply that the Strike Witch concept was being developed before the Neuroi arrived - either that, or the breakthrough came quickly enough to have the Strikers manufactured and rushed into hastily-formed squadrons in a mere two months. Or is there a big time gap between the novel's prologue and the rest of the story?
And as far as the current manga is concerned...