It it my impression that Oura has done a fair bit of work on validation of their measurements - when I looked into this 1+ years ago it really seemed they were doing more of this than whoop.
Here is one study regarding your question:
This is something that Oura almost certainly paid for or at least supported, but likely most/all device studies like this will be that way - they won’t be used in independent studies until there is some basis that they are doing useful measurements. I was involved in a UCSF study using the oura rings to see if it could detect COVID infections - I think the data from the 2nd part of that study are still being analyzed. I don’t know how critical the HRV readings in particular were to them using the ring, as they were using all the data collected by it.
I don’t know how this relates resting HRV, but the Tickrs are useless for collecting HRV during exercise - the DFA alpha1 numbers gathered from a ticker were meaningless in my case, and this seems a common experience. My numbers from the tickr has so many artifacts as to be way, way off. See HRV Logger FAQ - Heart Rate Variability Tools You may or may not be getting good numbers from your tickr, and I think you should be very cautious in regarding the numbers from the tickr as being the correct ones that other measurements should match.
On the sleep phases, I don’t think any trackers have good validations of sleep stages - those are guesses made from hand movement, etc. I have not seen good validation regarding this part of sleep tracking.