My advice is don't wait a few months and don't worry if they say "No for one is no for all". Just query them, one at a time.
They aren't going to say to each other, "Look out for this query, it's awful!" And unless you get a rejection from a different agent than the one you queried, chances are they didn't pass it on saying, "You might like this," either.
Just query. And query. And query. You have no way of knowing who might resonate with your work until it happens.
So: One at a time within the same agency, but no waiting period for querying another agent at the same agency (there's usually a 2 week to 6 month backlog in each agent's query queue anyway) after a rejection and no agency is so psychic that one agent knows what all of them are looking for.
My two cents.
That's poor advice. It does no good at all to query an agent who doesn't handle the type of fiction you're written, and darned few agencies have more than one agent for one genre. No matter which agent you send to, it will be passed to the agent who handles your genre, and she's already seen it.
And each agent does know what the other agents receive. If you think they don't talk to each other, don't keep lists of received submissions, don't all stay on the same page, you've never been inside an agency.
They know the query has already been seen by another agent, so, no, you aren't going to receive a rejection from the agent who has already seen it.
Unless more than one agent handles the genre you've written, and unless the agency says it's all right to query other agents within the agency, you're wasting your time, and you;re wasting the agents time, and writers darned sure can get a horrible reputation by poor querying practice.
And, yes, they darned sure do say, "Watch out for this query/writer. It's horrible."
They also say, "This guy wastes everyone's time."
They also say, "That's the fifth time this dummy has queried us with the same novel."
Some writers are known by every agency out there as time wasters to avoid. This makes finding a good agent nearly impossible.
Follow guidelines. Do as agencies and publishers request. They have reason, sound and solid reasons, for whatever policies they have in place.