I view it as this... your math is shitty ^^ (well DPCs math is too at this topic, but not as far off as yours) If it would be like you said, we were at 50% now, not 33%.On steam, on the latest news, and it's stated: "Season 3 is now 33% complete"
So, that must mean that he's viewing Zoey's intermission episode as one of the four that should be in S3. It would only be 33% if there's two more episodes to deliver from here, and so is the numbering going to differ from the expected 12, down to 11, and he's just roll with it (not four episodes per season, but whatever he wants now).
How do people view it?
So... no even DPC doesnt count the interlude as a full episode. There are still 3 episodes coming for season 3, like the season before we get 4 full episodes, but now the interlude on top, if you want to say it like that.
I would go with this math here... Interlude counts about 12%, episode 9 22%.... so 66% left, each eisode count as 22%... and we have the 100%.
Of course its not really a percentage-math-thing here. But yeah... its more like that... anyways, at the end... we have interlude + 4 episodes. Thats what DPC meant that we are at 33% of season 3, cause 3 full episodes are left. He could have called it a little better to be precise... but... *shrugs* And yeah its officially confirmed that we get 4 full episodes plus the intelrude in the end... so dont worry the interlude dont cut the season short.