When you upgrade your deck after a scenario, during a campaign, and you choose to upgrade a card (removing a lower level for a higher level version of the same card) do you pay the level difference or experience difference in XP?

Example: Does the upgrade of a level zero card to a level 2 card cost 1 XP or 2 XP? (Difference in experience (cost) is 1, difference in level is 1)

The latter seems to be more intuitive, but the rules reference (page 5) states:

- Each card costs experience equal to the card's level, to a minimum of 1 ( purchasing a level zero card still costs 1 experience ). The number of pips beneath a card's cost indicates the card's level.

- When purchasing a higher level version of a card with the same title, the investigator may choose to "upgrade" that card by paying only the difference in experience (to a minimum of 1) between the two cards and removing the lower level version of the card from his or her deck. (Emphasis mine)

Link to corresponding thread on BGG: http://boardgamegeek.com/thread/1670913/upgrading-level-0-cards/

You always pay the full cost of a new card and the removed card is not subtracted. Even if a level 0 costs 1 exp to upgrade it, you don't get refunded the difference. If I have a level 2 card and want to replace it with a level 4, I still pay all 4 experience, no discounts. This forces you to be careful with what cards you may want to just throw in your deck or remove at any point.

You always pay the full cost of a new card and the removed card is not subtracted. Even if a level 0 costs 1 exp to upgrade it, you don't get refunded the difference. If I have a level 2 card and want to replace it with a level 4, I still pay all 4 experience, no discounts. This forces you to be careful with what cards you may want to just throw in your deck or remove at any point.

That's demonstrably wrong, as the above example shows. If the cards have the same title and you're upgrading, you only pay the difference in level.

However if you're adding a card unrelated to another card (such as adding the Shotgun, which has no low-level version), you always pay full price no matter what you remove.

For the sake of laying this thread to rest, the corresponding BGG thread has gotten the answer from the source.

https://twitter.com/NatsunoYoru/status/797879584129744897

To upgrade a card of the same name, you take the level of the card you are buying and subtract the level of your current card. Pay that number in experience. You put the new card in your deck and take the old card out.

If you are putting something else in, you pay the level in experience. If it is a level 0 card, you must pay 1 XP - this is an exception to everything else. You put the new card in your deck and must take something out for it. You don't get refunded any XP for anything removed from your deck.

Looking through all the player card options, it seems the reason this is causing some confusion may be because none of the upgrade options in the core box are eligible for an xp discount as you're only ever upgrading from lv 0.

I guess I was off, same card names provide a discount, but outside of that, there isn't a discount for replacing leveled cards. So if I have a lvl 1 card and replace it with a level 3 card, I do not get a discount, but if they shared the same name, I do get a discount. Good to know, doesn't help with the core, but sounds good overall.