The Shop Manager currently handles shops on a per-event basis.
A shop is uniquely identified by two keys: a map ID, and an event ID.
This does not allow you to have multiple shops in a single event, especially if you want the shop to sell different things under different conditions (for example, a shop sells beginner equips at the start of the game, but near the end of the game sells advanced equips)
I am tempted to add the page number of the event to the key as well, but will have to evaluate the consequences. As long as you are not explicitly trying to grab a shop using `ShopManager.get_shop`, it should not be much of a problem, but there may be cases where you actually want to get a specific shop using script calls.
In any case, the next version of the shop manager will add the page number to the shop key. This change should not affect any existing shop plugins.