Has sleep detection accuracy improved?

I can see that there were some "issues" with the accuracy of sleep detection years ago, so in the intervening time, has it been improved?

I've just started using a Vivoactive 4 for health monitoring, and so far it has failed to identify sleep correctly - when I'm awake, doing some seated activity it labels it as light sleep, and when I'm asleep, it labels it as active, the whole night.

Is this just "early days" behaviour, while the watch learns about me?

Is it ever going to get better?

And on a related note, I've set up continuous SPO2 measurement.  The results for the first night showed an oxygen saturation that would be a matter for concern, averaging 90%; while the daytime readings (far fewer, because I keep moving) have been typically 93% to 95%.  Can I read anything into these?  Again, are they on a learning curve and will they improve over time?