What determines the update is the build number and the area and operator where the device is.
I have read also Paradoxa complaining about the CS asking him to clear the cache.
Well, this actually works too, but not always, in android devices according to many forums linked to android.
The most crucial info about the devices is the build number, not the TA-xxxx one.
Today I have received the security update for 01-2018. 97.3MB, (TA-1012, UK, unlocked, O2 sim card, Oreo 8.0)
I had a chat with the support and I was told to wait for Oreo and check sometimes. I feel like I just won't get any updates to my Nokia phone anymore. :-(
I tried factory reset on 2 SIMs, but no luck, my phone still gets no updates on Android 7.1. I wrote to Nokia support to ask about that, they say that they don't know when Oreo will show up on my phone in my country, and that the updates are a business of Google, not theirs.
The update is finally on my phone. It looks like something depends on them after all.