The Wright Brothers flew the first successful manned, powered and controlled aircraft in 1903, a feat which hitherto had not been accomplished, except by Santos-Dumont.
used in negative statement to describe a situation that has existed up to this point or up to the present time; "So far he hasn't called"; "the sun isn't up yet"
You use hitherto to indicate that something was true up until the time you are talking about, although it may no longer be the case. The polytechnics have hitherto been at an unfair disadvantage in competing for pupils and money. up to this time