I would have presumed the perceived gap was "yesterday we were using Julian, today we'll use Gregorian" (or Gregorian v0 to v1). Instead the article suggests it

I would have presumed the perceived gap was "yesterday we were using Julian, today we'll use Gregorian" (or Gregorian v0 to v1). Instead the article suggests it is "before today Julian and Gregorian both existed and were the same, now Gregorian has jumped".