What is the deadline for a US bank and the IRS to sign French Form 5000 a.k.a. CERFA 5000?

What is the deadline for a US bank and the IRS to sign French Form 5000 (mirror 1, mirror 2) a.k.a. CERFA 5000?

According to the Form 5000 instructions (mirror):

Unless otherwise stipulated in the tax treaty, French law stipulates that, in order to be valid, claims must be received by the French authorities by 31 December of the second year following the year in which the income was paid.

However, I don’t see any deadline for the US bank and IRS signatures on Form 5000, relative to when the income was paid. I have contacted some French bankers and I’m getting different answers: some say the deadline is within a few months when the income was paid, and some say the deadline is the same as for the deadline when Form 5000 must be received by the French authorities (which is 31 December of the second year following the year in which the income was paid according to the Form 5000 instructions). Nobody has been able yet to point me to a concrete text of law or evidence.

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Date of the US bank signature on the Form 5000 English version (a.k.a. Form 5000-EN):

Date of the US bank signature on the Form 5000 French version (a.k.a. Form 5000-FR):