Series numbering incorrect

[Luigi]

In this series:

https://www.goodreads.com/book/show/6...

Down to the wire is book #21, not book #20. And Whatever it Takes is number #20 but is missing.

[Sandra]

According to the publisher it is not part of the series, despite what amazon says.

[Luigi]

So, it's a standalone book?

[Camille]

Interestingly, the publisher skips #20 and lists Down to the Wire as #21.

https://www.penguin.co.uk/series/NSTO...