seasonal vault

Hi! i came back to play a few days ago and saw this seasonal thing, looking in the wiki it says that at the end of the season all items in vault are transfered to normal vault, thats ok, but this line got me thinking: "All Seasonal Vault expanders used are applied to regular Vault.", like, if i unlocked 3 expansions in the seasonal, that expansion is transfered to my normal vault, thats how it works?