if i understood rules correctly - each time a door is opened to closed
area(not visited by heroes before), there is a roll for room spawn.
Active token should be placed to such room to mark, that spawn was
done, but room was not yet searched.
I am bit confused by rules on page 8, next to active token sign, it
states - If all doors to active room are CLOSED and the room has not
been searched yet, place an active token in the room to show that area
is active & room spawns done.
is there any difference if room is closed or open?meaning - can active
token be placed even if 1 or all doors to new room is/are open?
It just means when you first check for Spawns because the door is opened or you have done a knock action place an Active token. Regardless of if you close a door or dont open a door after the knock test this room is active.
Zombies won't smell/see through a closed door but will take a route through one (open it at a cost of 1 MP) if it is in an active room and the shortest route to a character they can detect.