Terror in New York City - S1-E4
Character mistake: When Jeff is on the phone to Washington, thanking them for arranging the Sentinel to pick up Thunderbird 4 and take it to New York, the man in Washington replies, "That's the least we can do, Mr Tracy." So at least one person knows that Jeff is involved with International Rescue. This betrays the secrecy of the organisation that Jeff himself demands.
Terror in New York City - S1-E4
Character mistake: Inside the Mobile Radio Control Police Van, there is an "Ultra Short Wave" device that is labelled "Ulta Short Wave."