Past perfect that refers to a present perfect

[DirtyWater]

"I have updated the manual to include instructions on how to do XYZ. The functionality itself had already existed but it hadn't been documented properly".

Is the above grammatically correct?

In the first sentence I want to use the present perfect in it's stative sense to indicate that the manual is now updated, and the exact time when it was updated is not important, only the result.

In the second sentence I want to refer to events that happened before I had to update the manual. The existence of the functionality and it's lack of documentation are things that happened in the past, and the manual update is also something that happened in the past but later on, which made me consider the past perfect. However, I referred to the manual update event using the present perfect and not the past simple, as would normally be used with the past perfect.

Is such a usage possible? If not, what is the grammatically correct version of the aforementioned intent?

[Josef Essberger]

"I have updated the manual to include instructions on how to do XYZ. The functionality itself already existed but it hadn't been documented properly."