Watching for years and also focused on next June Europe/US trips I can honestly say there isn't any pattern when they open up R inventory.
For a while it started to look like every Friday or Saturday and then of course last week nothing
So you should always have a plan B or C. For me, my plan B was just to book award flights and just wait for R inventory to open up. Of course finding routes with award inventory is also something you can spend hours at, but be open to *A partner inventory also.
Being 1K I can cancel the award flights when R opens up. I'm not sure what the fee is for less the 1K members?
Don't give up and be creative flying anywhere over the Atlantic and then connect with a short flight in Europe.