First of all, you should understand the basic principles of handwriting identification. Handwriting identification is to find out the stable writing rules by collecting the handwriting samples of the parties, and then compare them with the handwriting to be tested to confirm whether they are the same handwriting. Usually two isolated signatures can't be compared, because a single handwriting can't reflect the stable writing characteristics, but it's not absolutely impossible. If two people's handwriting is natural, there is no disguise, and the writing level is obviously different,

Failure to find the signer is not a reason to refuse the appraisal. If so, the will can't be authenticated? However, it is difficult. As mentioned above, because the appraisal needs to provide comparison samples, and the samples can only be used after the litigants cross-examine them in court, the appraisal institution is not responsible for the authenticity of the samples. However, the court can also take samples according to the application of the parties, looking for uncontroversial signatures written by the signer before, such as marriage registration, replacement of identity cards, notarial certificates or house transactions, or there is evidence that the handwriting is written by the signer, which can be used as samples for identification. To overturn the appraisal conclusion, the other party must first prove that the signature above is false. If you can collect a written sample of the signatory, the court has no reason to refuse the appraisal.