My great grandmother Lizzie M. Adams sold her patent (number 680,106) to C. H. Munson in the early 1900s, I think. I have a newspaper article of the sale but no date.
Patent sale date can be determined in following ways:-
- Check the respective patent office Patent Register e.g. US patent USPTO Assignment Database
- Check online News Articles or Press releases.
- Contact the attorney of the Application
- Contact the inventor/applicant of the application
Now to query you cannot find it in online database as case is too old and if patent office direct contact doesnot provide you concrete information than you need to contact publisher of newspaper for date. Most likely it should be enough.