Could anyone help me with this issue;

I want to determine if the dates of an combination of product & customer are overlapping each other.

I think im close, but with the following formula I get an error:

=COUNTIFS(C2:D5;">="&C2;C2:D5;"<="&D2;A2:A5;A2;B2:B5;B2)

This is an simple example sheet where I used the formula (product nr in cel A1):

Product nr | Customer | Start week | End week | |

5544556 | Peter | 5 | 10 | #VALUE! |

4455665 | Mark | 4 | 7 | |

5854545 | Mark | 7 | 12 | |

5544556 | Peter | 6 | 9 |

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Any help or suggestions are welcome.

Thx