You make an excellent point and you are very likely correct on the matter concerning the two signatures. However, for the sake of discussion, in case the inevitable questions reqarding them arise, allow me to play 'Devil's Advocate' on this.
Could it not at least be conceivable for Madelyn to have gone to the local registrar's office and provided the required information to be typed onto the form. She could then have stated that her co-signer, Martin Blaine E-?-n, was busy with clients, customers, meetings, sickness, or whatever, and could not come in personally. She, however, would be happy to take the form to him for his signature and return the same day to the registrar's office to complete the process.
Regarding the above 'forgery' scenario, IMO -
Loosey goosey and unlikely? Yes!
Impossible? No! (But this wouldn't invalidate the authenticity of the document)
THERE IS NO CERTIFICATION ON THE FORM THAT EITHER OF THE SIGNATURES IN BOXES 18a or 19a WAS WITNESSED BY ANYONE.
I wonder if an image of Madelyn's signature is independently available anywhere on the web? I looked a bit for it but couldn't find anything. It would help authenticate the document if her signature could be shown to match that on the Blaine COLB application.
In my reconstruction of the clerical procedure in the local registrar's office and given to explicit attempt to prevent fraud in the language of HI Law 57, the clerk's signature is, in my view, almost certainly intended to be a witness signature of the employee of the state of HI to the signatures and representations of the witnesses.
As you suggest, obtaining comparison signatures for Madelyn, especially to see whether she dropped the “e” in her name on occasion, would be good!