The bug description is slightly misleading in that the bug was arguably a UI issue rather than a storage problem. Non-localized dates displayed in a date picker would jump to the UTC value whenever a new value was submitted and the user left the field. This was entirely visible to the user and happened before any database interaction, giving them the opportunity to correct the problem.
However, assuming your users are not all Hawk-eye, it is possible a user may have missed the jump and saved anyway. In this manner some data may have been submitted with an offset of your time zone.
Just to emphasize: this only pertains to non-localized dates rendered in editable date pickers. All your other date values are fine.