This is an excellent question Ash and we looked at it in great detail.

That's what we believe -

Often English speakers avoid using the past perfect as it can sound awkward in English unless the previous past action it refers to is in the actual sentence which is not the case here.

In this colloquial expression, "I told you so! " strictly speaking, it should be "I (had) told you so!".

The wife in the story had told Rémi to update the GPS and even to buy a new one so in French it cannot be anything but the plus que parfait -

Je te l'avais dit !

But thank you for this excellent question which got us thinking ...