Say you have written manuscripts A, B, and C (A being your oldest written, and C your newest). You are lucky and land agent with manuscript C. Would an agent look at manuscripts A and B at all? Is this decided by how recent they were written, or if the author wants the agent to also look at them? Just curious over all, how does this type of thing work and what factors play a role in these types of decisions?
When I sign a client for a Shiny New Novel, one of the things I do ask about is inventory. If you have inventory, and you sign with an agent, you tell her about it.
Most likely she's not going to read any of it while her hands are full with Shiny New Novel.
If Shiny doesn't sell, then I look at inventory.
Chances are inventory isn't going to sell either, so it's on to New Book.
There's no way to quantify this because every writer has different inventory, and agents work differently. This is why you want good clear communication with YOUR agent. Ask HER what she wants to do.
I've sold inventory novels. I've flat out refused to look at inventory novels after hearing about them. There is no one answer here because the question has four dimensions: the author, the agent, the book, timing.
You thought three dimensional chess was tough? Add time as a factor and you've got a good metaphor for this.