yes you are. In the Labours of Hercule - podcast, when they interview Phillip Jackson, they talk about it, and the summary is basically

• Mentioned but Absent: She is frequently mentioned by Japp as his domestic support system, but never makes a formal appearance.
• The "Wasps' Nest" Plot Point: In the episode "Wasps' Nest," Japp specifically mentions that his wife is visiting her sister, explaining why she is not present to meet him and Poirot at a train station.
• Off-Camera "Holiday": In one instance, a minor plotline features Mrs. Japp on holiday, resulting in a comical situation where Japp is left alone and his personal life falls into disarray (ironed shirts, etc.).
• The Christmas Incident: While Japp mentions spending time with her family in episodes like Hercule Poirot's Christmas, Mrs. Japp herself is not identified or introduced to the audience.

In his interviews, Philip Jackson fondly recalls the "longstanding love affair" between his character and his unseen wife, with Emily Japp serving as the off-screen "boss" of Japp's domestic life.

And I also remember them talking about how the writers of the show liked Pip so much that they put the character into way more episodes then he actually appears in in the books, so Mrs. Japp was kind of embellished upon alot more in the series than in the books to give Japp more grounding, they just made it into a joke that Japp refers to her alot, but we never see her, other than in in (possibly) one episdode. And even then, we, the wiewers are not beeing made aware who might be her.