A spouse-related exception may be relevant, but its conditions and the accompanying or following-to-join arrangement require review. Separate applications are not proof that the exception applies or fails.
Resolve the household sequence before relying on it
A qualifying spouse and unmarried children under 21 must also meet their own derivative requirements, including applicable age protections. Chargeability does not grant family status, and the principal must immigrate before or with the derivatives under the applicable process. Decide what the household will do if the exception is not available, and decide it now rather than when the answer arrives.
That contingency is the real content of this question. If the plan without the exception remains workable, meaning a longer wait, the same investment and the same eventual outcome, then relying on the exception is a matter of speed and the downside is delay. If the plan without it collapses, the household is depending on a legal conclusion nobody has confirmed, and obtaining that confirmation becomes the first priority rather than a step in the sequence.
A second timing point belongs alongside it: derivative children must satisfy the applicable age requirements, and the applicable age protections are calculated rules rather than a general allowance. A family relying on both an exception and an age calculation is relying on two determinations at once, and should know which of them is the more fragile.