It certainly adds possible fuel to it.
Which is to say, it's quite clear that ponies talked the same a thousand years ago. So, most likely Royal Canterlot Voice was only ever a thing for Royals in Canterlot, specifically for talking to their subjects.
The only question is whether Celestia failed to remember this, as it was a thousand years ago and she hasn't heard Royal Canterlot Talk for a thousand years, or specifically didn't say because Trollestia. I'm not convinced there is a third option.
Also, yeah, I've aparently totally head-canon'ed the thing where Celestia considers everything longer than a couple of decades or so to be A Thousand Years Ago.
EDIT - Hey any questions yet Strife?