There are $7$ balls in a jar, numbered from $1$ to $7$, inclusive. First, Richard takes $a$ balls from the jar at once, where $a$ is an integer between $1$ and $6$, inclusive. Next, Janelle takes $b$ of the remaining balls from the jar at once, where $b$ is an integer between $1$ and the number of balls left, inclusive. Finally, Tai takes all of the remaining balls from the jar at once, if any are left. Find the remainder when the number of possible ways for this to occur is divided by $1000$, if it matters who gets which ball.

Let's think step by step and output the final answer within \boxed{}.
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