I do not have a Citation, but, my understanding has been, that anything "fifty years old' or older, is good to go for C & R ( so long as it is not some 'any other weapon' or a sawed off metallic Cartridge Shotgun having barrels less than 18 inches, a selective fire with full auto option, and so on along those lines ).
Thus making all Original run m1911s good to go under the C & R.
Reproduction m1911s, would not be good to go under C & R. since they as individuals are not older than fifty years of age.
Why do you distinguish the "1918" from the "1911 Model O"?
1918 is merely one year among many during which the m1911 was produced. There is no Model of 1918 or 1918 designation.
All circa 1918 Colt .45 Automatics, would be Model "O"s and all Colt .45 Automatics made in 1918 would be ether 'm1911s' or Government Models.
So, in summary, far as I have always known, any Colt .45 Automatic in original configuration and not modified to go full Auto and not having a Smooth Bore Barrel, and not fitted with a 'Silencer'...if it is fifty years old or older, it is qualified under the C & R FFL.
Some 'Commemoratives' less than fifty years old, may also qualify, but, for that, one would have to consult the B of A T F and now also E "List" of individual Arms which are less than fifty years old, to see if the one which one may have in mind will qualify under C & R.
And if not, one can always Petition the B of A T F and now also E, to have them add a 'Commemorative' they had previously overlooked.