@chris-bouffard There is very little in boundary surveying when it comes to found evidence and making decisions based on it that will leave you feeling absolutely certain. Certainty, confidence, and the strength of your professional opinion always comes in degrees.?ÿ?ÿ
The cap is gone, the remaining portion of the monument is of the same type and character as described on the record map, if it appears by the amount of rust & such to be about the right age, if it fits reasonably well with nearby monumentation that you have a higher degree of confidence in, then it is most likely the original monument for that corner.
There's a lot more than matching what you find to a record description when analyzing found monuments.?ÿ Recognizing when the evidence is strong enough to support your decision is, to paraphrase aliquot, what separates the professional from the technician.