Well corporate contract says/explains a lot!
I don't think they would be so generous proactively if you were a solo traveller in D/I class.
I know someone who recently got upgraded from SL to GO at only around 400TP. She is just a housewife flying one long haul and few short haul per year all in paid J, D/I class. On the other hand, her husband, who flew roughly the same but with one less short haul, got no upgrade offer.