Checking back in to add my datapoint. Thanks taway for taking the time to answer my questions! Much appreciated.

We are in Canada and were able to access OLCI at T-36 hrs. (Route was YUL-LIS-FAO-LIS-YUL, we were flying economy.) On our return, we had a 24 hr stopover in Lisbon, and I was surprised that at T-36 the FAO-LIS flight, the final leg (LIS-YUL) was also available for check in, a full 60 hrs before it was scheduled to fly. I expect connecting flights to be generally available at the same time as first flight for OLCI, but with that long a stopover, I was a little surprised that the full itinerary was open.

On all four flights, yes, we had been assigned seats together. There was some weirdness with the boarding passes, in some cases the seats weren't shown, but were visible on the app, and in one case we had something like seats D & E at OLCI but E & F in the same row at airport checkin. Weird, but not significant. 3/4 times the seats were fine. Not the best, not the worst, so I had no need to try to change in that small "open" window before take off. On the 4th flt, as OLCI opened, we had been assigned the very worst seats on the plane. You guessed it, back row, no recline, right next to the toilets. That takes a special kind of malicious algorithm. I had had enough of TAP's shenanigans at that point so I paid to buy two seats further up the plane. To add insult to injury, when we took off, the flight was maybe 70% sold, and the moment they closed the doors, everyone got up and found a seat they liked better. Honestly, the flight crew was great, we didn't have to share our row, and I'd had a great lunch in Lisbon, so what are you going to do at that point, other than sit back and enjoy the ride?

FWIW, I won't chose TAP again if I can help it; as all the questions and responses here indicate, there is too much trouble understanding how things work, and too many practices that are more LCC than national airline. Between checking baggage (when I actually carried less than on our last trip to Europe, when we flew LH carryon only), to avoiding being assigned the actual worst seat on the plane, oh, and then there was the 4 hr delay with no information and no staff available to talk to--yeah, no.

But again, thanks for the help of this forum, and happy travels to all.