I see where you are going and understand the appearance of redundancy; however I tend to give the Passport Office the benefit of the doubt here.

If the requirements had not had changed from when your child’s passport was first issued, and details of the birth certificate noted, I would tend to agree with you.
However the new requirement:-

Effective February 1, 2008, 22 C.F.R. 51.1 requires that U.S. passport applications for children under the age of 16 require both parents’ and legal guardians’ consent.

Gives new meaning to how the ‘birth certificate’ is used. The process of recording and auditing this information now has to pass a higher threshold if indeed the passport is to be used in place of the birth certificate to establish relationship. Also the difference between guardian and birth parent has to be explicitly recorded.
As I stated I feel this example is not a clean one, in terms of your point, although I accept the underlying principles you are articulating.

If the supposition in the bureaucracy is that the parents’ appearance, pictures, and names align with the child’s named parents (on the birth certificate), and instead of providing a birth certificate, the re-application includes all the same information + the prior passport + the appearance of the parents with their IDs, then there is no operational difference between a prior passport and the birth certificate since the prior passport established everything in the first place.

The failure of this procedure is that it assumes names don’t change over time and/or that identities aren’t stolen.

Since the birth certificate is only a reasonable level of assurance, not a guarantee, then for the majority of situations, the prior passport is just as reasonable an assurance.

I suspect, however, that I/we and the DOS (and those in the child-protection field) might disagree on how we respectively define “reasonable level of assurance”.

We’re TOTALLY in favor of ensuring children are positively identified with their rightful parents/guardians, and our only point in bringing up this post is that given the holes in the procedure and combined with not-uncommon situation, the procedure was too restrictive and doesn’t account for variation in the possible inputs defining the scenario as the business rule is applied.

Feel free to disagree, but it is possible to “write tests” that the procedure, as it currently is defined, will fail in two modes: (1) bad input still produces outcomes within expected ranges, and (2) a subset of good input causes an unhandled exception.

That’s the whole point, all of the documents establishing the link from the birth certificate to the current ID of the guardians needs to be presented each time a passport is granted for a minor.

There are many issues with ID thefts etc. but I see no reason to alter this process of establishing the current child’s guardians by linking to the legal documentation trail to the birth certificate.

“but how does anyone know that unless they review the child’s Birth Certificate and evidence of the current guardianship status.

If your argument (more to the point, your defense of the rule) were to hold together, the child’s birth certificate also wouldn’t establish evidence of relationship.

And, in our case, both parents were present, and, the prior passport used the same evidence as what they required the first time, as though he didn’t have a passport.

In other words, the process designers didn’t validate their requirements (i.e., make sure the requirements withstand the test of the actual user environment). So, while they may have declared their Business Rule or Requirement of the Process “valid”, they did so without actually testing to see if it holds together. In other words, it wasn’t truly “valid”.

It is to do with the new requirement that both parents have to give their consent for a minor to have a US passport. This came into effect recently, I think Feb 2008. Anyway bottom line is
“Previous U.S. passports are not acceptable as evidence of relationship”. You can go thru the divorce name change arguments etc. but this fact holds (for the process designers) and as such is a valid Business Rule or Requirement of the process.