This is a great write up, thanks so much for taking the time.
I found it impossible to release the upper tab. This tab is situated so it is impossible to access. I'm not certain if you were able to open it with brute force or if you had some other trick. But in the spirit of paying it forward…
If you drill a small hole roughly 5 mm behind the edge you can then use a small screwdriver to push down on the tab directly and it will unlock. While drilling a hole in your instrument cluster is not sound very desirable, at least the hole is located in a spot you will not be able to see it once it's installed back in the vehicle, as it is covered by the shroud that sits above the overall cluster.
Hope this helps the next person :-)