Board Game Arena

See the FAQ for an explanation on the ELO-calculation: https://boardgamearena.com/faq?anchor=faq_account_elo
ELO does not take luck into account. In other words: part of your ELO going up or down in a game is because of luck, but in the long run your skill will determine if your ELO goes up or down.

From the catan.com faq:

May I play a Progress Card if playing it has no effect?
If you know beforehand that playing the card will have no effect (e.g., the Mining card, provided that you are not settling adjacent to a mountains hex): no.
If you have no way of knowing it (e.g., Trade Monopoly): yes.

I agree, separate game, separate ELO.

Yes!