Season 6 so short?

Because, for financial reasons, there was a break in production between the 16 episodes that make up series 5 (January - May 1967) and the 8 episodes that make up series 6 (September - November 1967). If that hadn't occurred it would have been a 24 episode series.

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Sparks Moran: "It was dusk. I could tell 'cause the sun had gone down"

What is shown here and some other places as "Season 6" is just a few repeats. It wasn't actually a new season of shows yet.

I'm sure you can find why it's listed like that somewhere.

There are 6 "series" of new seasons / shows.

Not to be too confusing, but the real "Series 6" is shown on places like this as "Season 7" - with "Season 6" being a small number of re-runs of earlier shows.

It must be that they hadn't made new shows yet and so played re-runs a while and end up calling that Season 6 some places or something.

The Emma Peel episodes from Return of the Cybernauts to Mission Highly Improbbable were shipped off to the US along with the first 7 Tara King episodes including the Forget Me Knot. This made up one whole season. Then there was a break and the next US season the final season consisted of the last 26 Tara King episodes.