When an event in the game triggers multiple effects, are these deemed to happen simultaneously, or, can I trigger them sequentially in whatever way is most advantageous? Some of examples to clarify what I mean:

1) Darrel Simmons obtains a clue from a research enquiry and completes his Personal Mission. As the immediate benefit of this, he gains three clues. He still has his "seek the truth" task asset. Can he spend the clues he just gained from the Personal Mission to complete the task?

2) In a game where Yog Sothoth is the AO, an investigator defeats a cultist monster. This means they lose a point of Sanity and gain a spell. They also have an asset which allows them to regain a point of sanity if they defeat a monster (like say the Lodge Researcher ally). Can they therefore take the sanity loss and then immediately gain it back again?

Also, for those Task Unique Assets which require some form of token (usually Eldritch Tokens) to be placed on them, is there any limit to the number you can add per round if you successfully complete the required action? An example would be 'Sealing the Old Ones', where you could in theory succeed in the Lore test needed for a spell and then discard it several times per round. I seem to remember reading once that there is a limit of one token per round, but can't find the reference.

Without saying anything about the specific situations you mention I would say this. The language is very important, some times things don't happen simultaneously that at first may seem to happen simultaneously. But that said when things happen at the same time the active investigator decide in what order they happen (so in a way they still don't happen simultaneously).

I have no recollection of a limit of one token per round on task fulfillment and haven't played it that way, but may have missed something myself.

7 hours ago, Elder Thing said:

1) Darrel Simmons obtains a clue from a research enquiry and completes his Personal Mission . As the immediate benefit of this, he gains three clues. He still has his " seek the truth " task asset. Can he spend the clues he just gained from the Personal Mission to complete the task?

No, he can't. Those clues weren't gained "during" a Research Encounter.

7 hours ago, Elder Thing said:

2) In a game where Yog Sothoth is the AO, an investigator defeats a cultist monster. This means they lose a point of Sanity and gain a spell. They also have an asset which allows them to regain a point of sanity if they defeat a monster (like say the Lodge Researcher ally). Can they therefore take the sanity loss and then immediately gain it back again?

Yes, they can.

7 hours ago, Elder Thing said:

Also, for those Task Unique Assets which require some form of token (usually Eldritch Tokens) to be placed on them, is there any limit to the number you can add per round (...)? An example would be 'Sealing the Old Ones' (...)

There's no such limit unless a task specifically mentions it. Some do . Sealing the Old Ones doesn't.

13 hours ago, tsuma534 said:

21 hours ago, Elder Thing said:

1) Darrel Simmons obtains a clue from a research enquiry and completes his Personal Mission . As the immediate benefit of this, he gains three clues. He still has his " seek the truth " task asset. Can he spend the clues he just gained from the Personal Mission to complete the task?

No, he can't. Those clues weren't gained "during" a Research Encounter.

That's not quite right - the "during a Research Encounter" only refers to the triggering event that allows him to spend the three clues to complete the tasks. Where he got the three clues he spends does not matter, he's just not allowed to spend the three clues for the effect anywhere except right after he gains one during a research encounter. The question is more about the timing. All of these effects are being triggered at the same time, so it's referring to the resolution of the effects.

1)He gains a clue during a Research Encounter

2)He places an eldritch token on his personal story and simultaneously spawns a clue per the "seek the truth" task asset as WHEN effects triggered by those cards

3)His personal story now has enough eldritch tokens to trigger the reward but he does not yet have three clues total

4)Both his personal story and "seek the truth" now have THEN effects to be triggered
- his personal story gains him the reward card which immediately gives him 3 clues
- "seek the truth" gives him the option (MAY) of spending 3 clues, discarding it, and advancing the mystery

Whether the clues spent were gained during a research encounter are irrelevant - the primary question is: Is he allowed to resolve the personal story effect that gives him the 3 extra clues before he triggers the option of spending 3 clues on the task asset, OR... because he didn't have 3 clues at that exact moment, is he prevented from exercising the option on the task?

Seeing these timing points, I would say you should be allowed to resolve in whichever order, allowing you to use the clues in that manner.

Thank you very much to all who responded. You have clarified exactly the issues I was unclear about. Your comments regarding paying attention to the precise language with regard to the triggering of effects are particularly useful. It looks like I've been handling this correctly during play, but, as I said in my original post, I couldn't find a reference clarifying it anywhere in the rules (checking both the original base gain Rulebook and Reference Manual). Does anyone know please if there is such a reference?

With regard to the question regarding Task Assets again, I do seem to remember once seeing a clarification stating that more than one player cannot add tokens to a Task in one round. This would in theory be possible in the form of Player A succeeds in the task and then performs a Trade action with Player B, who then also attempts the task. Is this prohibited, or am I misremembering?

I have a further question. With the obvious exception of those marked 'once per round', I have always assumed that there is no limit on the number of times a given possession can be used during a round. So for example, a Binding spell could in theory be used for every Combat Encounter during a round. Is this correct please?

Many thanks for any help.

Yes, but rerolls may only be used once for each dice roll if not stated otherwise.