Yes, it kept changing during my period of looking for a booking too.
I starting looking for flights to Europe and back for Summer 2022 just over a month back. Mainly from MEL, but I also had a scan of flying out of other cities. So UK, France, Italy, Spain, Germany, Switzerland were all looked at.
I was being flexible and so was looking at anywhere in from May onwards. I was looking at 7-10 weeks in Europe. I was looking at both flying in and out of the one airport, as well as my preferred option to fly in at one airport and out of another.
Initially I could find many options to Europe to many different SQ Airports. But you could only book waitlist for return flights. 
If nothing opened up in the near future I was going to book flights there and just hope that flights would open up sooner or later for the return.
Late at night on round about the 25th Sept (may have been a night earlier or later as I just remember it was the weekend) all of a sudden bookable flights back to Australia were there. But only as return flights, and not one ways.
You beauty I thought. As it was late, I decided to discuss options with the wife the next morning and book then. We picked Paris, as while we could book London the return flight from there had the very hefty extra taxes. But on logging in it had reverted back to no bookable return flights to Australia.
I checked again the following weekend and while there were date gaps there was from MEL plenty of J flights to multiple cities in Europe, both one way and return.
So on 2nd Oct I booked one way J's MEL- LHR in June and CDG-MEL in August. 
