However over the past few years "actual value" was bringing a smaller percentage of the appraisal value than three or four years ago when the economy was better.
Defacing a vintage instrument is never a good idea, as even an authentic signature will usually hurt the collector value.
There are three pages in total: 1950's, 1960's and 1970's!
This PDF file has the infamous "JASS BASS" misspelling on the warranty registration card which is on page 12. This file came from member "Bassclef" at the Fender Jazz Bass Forum. This page is a gateway to a wealth of information on vintage electric basses by Fender, Gibson, Rickenbacker, Hagstrom, Gretsch, Hofner, Epiphone, Guild, Harmony, Vox, Ampeg, Danelectro and Kalamazoo. Very educational and very fun site with tons of historical information. - Fender color offerings changed periodically which can help with dating.
My advice is not to buy a celebrity signed anything, vintage or otherwise, without authentication that the autograph is in fact genuine or proof that it is the artist's signature.
Proof could be a photograph of the artist signing the instrument or a photo of the owner with the celebrity while he is signing it is even better.
Also knowing the appraisal value gives you a starting point for setting a price to sell an instrument, plus you will have an accurate and authoritative description to use when advertising it for sale and can quote the appraisal value and appraiser's name.