Developing a Sharepoint application would have all the fun of a video game, if only you had infinite lives.
Unfortunately, that makes your project like the Titanic.
Although asynchronous events expose a SPItem Event Properties parameter named properties just like their synchronous counterparts, remember that the operation has already completed so you cannot modify anything in the properties parameter (well, you can, but it doesn’t do anything).
Additionally, the properties parameter may not be populated with information that you would tend to expect to be present.
the actual Add / Update operation for which the Adding / Updating event is being fired).
Do NOT try to manually get the list item in code and update a property on it because the optimistic locking mechanism in Share Point may throw an error later on when the operation associated with the event to which you are responding attempts to complete.