Not all craft in the field have all options or even the same equipment. Also just because we model something one way doesn't mean the next one along is an "upgrade" very often it really wasn't . See the N11 N16 example above, or try the D.H.5
Sometimes sights were removed if they actually made the view worse for example or pilots found they cracked their head on them in a crash etc. Some craft in OFF have field mods, or rare parts whatever as it is deemed fun/useful/interesting whatever,or to stop the modeller from dying of boredom ;)
The stats may be wrong, why not fly them all and test - after all what counts is what it does when you fly it ;) ?
Given wings, and tail parts and all sorts are swapped, also don't forget one craft that is meant to be exactly the same as another often would have differing performance in climb rate or speed on the field down to manufacturing, engine performance differences, setup etc ..
Once you try to explore WWI it's a can-of-worms I tell you ;)