The large digit "3" at the rear of Thunderbird 3 always reads left-to-right, regardless of whether the spaceship is flying towards the left or towards the right. It is assumed that 2 different models were used, since when the spaceship is rising vertically with 2 of the 3 sides visible, the "3" digit may appear in either orientation.
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.
If a rocket as powerful as Thunderbird 1 were to be launched through a swimming pool, as in the series, the pool would vaporize, destroying it completely, along with the nearby Tracy House.
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).
There are some episodes in which civilian personnel who are being assisted by International Rescue call a Tracy brother by their first name or refer to them as "Mr Tracy". How would they know their first and last names? International Rescue is supposed to be a secret organization and they shouldn't be telling people their names at all. This of course could all be accounted for by them talking to each other by their first names when on a mission (but they still shouldn't know their last name), which is something they shouldn't be doing if they want to keep their identities and the location of their base a secret.