Revealing mistakes: In five episodes, there are newspapers with the date Friday, 24 December 1964 on the front cover, and was clearly not intended to be seen by viewers. (Oddly enough, 24 December 1964 was a Thursday).
Plot holes: There are some episodes in which civilian personnel who are being assisted by International Rescue refer to the Tracy brothers by name. How would they know their names? IR is a secret organization and it's highly unlikely they would give out their names.
Continuity: In all episodes that show Thunderbird 1 taking off from Tracy Island, the launch sequence contains a major error. As TB1 descends the ramp to the launch bay, the wings are at right angles to the direction of travel. As it emerges from the tunnel, the wings are aligned in the direction of travel. In other words, the craft has rotated 90 degrees as it goes down into the launch bay.
Revealing mistakes: No matter what time of the year it may be, every newspaper in the series with a date seen on it has a December 24 date.