So, you expect all characters to know everything all the time. Does that really seem reasonable or realistic to you?
I agree. People forget that the Federation takes something like eight weeks to travel across using warp speed. If something happens on side of the Federation, it's not a given that everyone knows about it merely because it happened. The Doctor was a specially designed program and wouldn't necessarily know everything about Starfleet's first-contact missions or military engagements.
The Federation didn't start to compile medical information about Jem'Hadar until Bashir worked with the Jem'Hadar adolescent in "The Abandoned." That doesn't leave much time before Voyager