Sometimes I wonder about statements like that.
One would think they would know from the beginning so they can prepare themselves by trying to get into the mindset needed to be the character.
Conversely an interview I read about Shipp indicated that he wasn't told until they were well into Season 2 that he was to be Jay Garrick and that the news was sprung on him.
Sometimes TV writers don't even know themselves which direction they are going to go until later in the season. Which is why you sometimes get stories that don't fit well together or seem inconsistent if they change too much in the middle.
One example is Supergirl and that Hank Henshaw was supposed to be Hank Henshwaw... until they decided later on to make him a martian.
Smallville and Charmed are two shows where I remember years where it seemed like they made things up as they went along, which made for disjointed plot resolutions.