Hi!
It seems like the constraint checker could check for
either only one
"Preferred" or all but one "Deprecated" which would allow editors to
evolve in whichever way they wanted.
It should probably consider "best rank" ones - i.e. if Preferred exists
then Preferred ones, otherwise Normal ones but never Deprecated ones.
--
Stas Malyshev
smalyshev(a)wikimedia.org