I can honestly say from experience is never take Springhill's suggestions as an example. Have you grown the ones from SH or saw them in person?
It seems from Old House Garden's explanation they are finding some Glads are hardy outside previous normal conditions. No doubt because of our global warming.
It seems that Priscilla, according to White Flower. can be added to the hardy list. I have had pretty good luck when they give a zone that they have at least tested the plant to be sure they are not giving bad info.
Oh well as gardening goes I guess we can never say never. All things are possible with gardening. It is fun.
