Intelligentsia - hmmmmm. I notice you haven't had many takers.

First, I don't have a clue what the NPK might be for decomposed needles. But will they contribute to the acidity of the soil - Yes.

Any organic matter (leaves, needles, twigs) falling around plants and onto the soil will release organic acids as they decompose. When the accumulation is greater than decomposition, an acid condition follows.

It's natures compost. And I fertilize nothing once planted in the ground, but make sure my beds have an added layer of compost every Spring, sometimes reapplying in Fall.