Many of my father's clients have asked me for authentication papers for their works. My father kept good records throughout his life. Usually I can find the old invoice by correlating his numbering system on the work with the invoice #. His numbering system and his signature, ESPENET, always confirm the work. I charge $200.00 for the authentication process. The numbering system is as follows: the first two #'s are the year. The second two #'s are the sequence of work for that year. For example, 6097 would mean 1960 and the 97th piece made that year.
Concerning appraisals, I may have a ballpark idea of what something is worth currently but I refer myself to experienced appaisallers . Please refer to them.