Usually a TV series will have a 'bible' which gives descriptions of characters and their motivations, will sketch out plotlines and generally serve as a guide for writers/directors, actors and anyone else involved in the production of the thing. Often, but not always, a bible will cover a season at a time.
Either GW doesn't have one or no one reads it. It's also entirely possible that they're just flying by the seat of their pants with what seems to be heavy nudging from Hallmark Corp to not do anything which could possibly offend anyone.
Also, could just be that the production company made the first movie, it did well, they expanded it to a series, added some more films to fit it--more or less--with the series and kinda shrugged about plot holes.
That's what I think, anyway.