In tinker Bell 1, after the talent ceremony, Tinker Bell is escorted to tinker's Nook. On the way to Tinker's Nook, they passed through Winter Woods and saw the Winter fairies come back from bringing Winter to the "Mainland", so all the rules about winter dating back from "before Tinker Bell" makes no sense.
In Tinker Bell 1, there appears to be 6 siblings born of that laugh. tinker bell fell behind by bumping into a bell.
In Tinker Bell 1, winter fairies were present at the talent ceremony in "summer"
When Periwinkle is re-visiting the past, high up in the air on the snow-flake pedestal, Lord Milori comes and joins her to tell her a tragic story of the past. It is later revealed that he cannot fly anymore, so he couldn't visit her there without aid. No such aid is visible.
A pivotal plot point of this film is that the fairies from other seasons can't enter Winter and Tinker Bell goes to great lengths to visit there for the first time. However, in Tinker Bell 2008, which this is a sequel to, Tinker Bell, Bubble and Clank happily fly through Winter without a problem.