Bleached hair getting darker again - is that even possible?

In December last year, I had my hair bleached from a dirty blonde to a more golden tone. It was definitely bleach - the hair stylist said it was, I saw the product, I smelled the product, I felt as some of it was touching my scalp. The result was quite significantly lighter than my previous color.

Fast forward, I’m starting to realize that my hair looks darker again. And I don’t just mean my roots. When I cover my roots with my hands, the rest of the hair still looks darker.

I have checked every product I use, and none of them have pigments - except for the purple hair mask which I have used from the beginning to combat yellow tones.

I thought I am imagining things, maybe I just got used to the new blonde,…? So I checked old photos from before and right after the salon visit, and I’m not imagining things. My hair really was a lot lighter in color after the bleach than it is now. It is still brighter than the dirty blonde that my roots have, but a lot darker than right after the result.

I am so confused.