The Mail used to have a specialist defence & aviation correspondent but that slot disappeared back in the mid-1990s.
As mentioned above, there are the specialists and the general reporters (hacks). ALL of them are generally subject to the whims (and, in some cases, prejudices and general ignorance) of whoever is running the news desk - home or foreign - that day.
This can then be compounded by the subs desk. Time was that a sub would ask the correspondent to clarify something if the sub was not sure of either meaning or sense. Nowadays, it frequently looks as if this is no longer the case.
One other thing, I do not know about other papers, but I do know that if you see a piece in the Mail bylined to "Daily Mail Reporter", this is shorthand for "This Piece Has Come Straight From Agency" e.g. Press Association.