When I eventually ranked up to Trainee in ToT (and got the Orichalcum rewards) , the season progress reported 0 / 1000 Tribute XP (unfortunately I didn't screenshot it).
The next time I looked, without playing anymore ranked games it stated 500 / 1000 XP. Maybe this was a result of the placement matches, but as I finished 1W-4L I'm not so sure.... It looks like so...

Then I win a game, gaining 210 XP, but here's the first issue. The match rewards tally is reported incorrectly as 1210 / 1000. As below (I know the other rewards below the line are another outstanding issue)

Confused (I was...), I checked the rank screen again which shows 710 / 1000, a more sensible use of addition.

So, to summarise, the match victory screen shows the wrong XP progression, and I don't know where my initial 500 XP came from.