Basically, depending on the order you set your enchants, you can reach a point where you will be stuck with 2 remaining points out of 12, even if the remaining enchant would replace an existing one (i.e. : the Quality)
Some enchants being replaceable by a better one, this should be taken into account regarding remaining points on an object.
Repro:
My repro uses Resolution (unique Sabre)
It comes with 6 points used.
Annihilation (2)
Reliable(2)
Fine (2) - replaceable
"Wrong" Order:
-set Secondary Damage (2 points)
-set a Slaying - non Kith (2 points)
-you end up with 10/12, and you cannot replace Fine (2) with Exceptional (4), even if the real cost of Exceptional is (2) (Exceptionnal replacing Fine).
"Right" order:
-set Exceptional first (actual cost: 2)
-you now have 8/12 points used
-set Secondary Damage (2)
-set a Slaying - non kith modifier (2)
-have a 12/12 weapon