This is a remarkable specimen with an unbroken chain-of-ownership (President Johnson-to-Congressman Stephens-to-DrDarryl). As you can see the number of "-to-" is two ! (I have two degrees of separation from President Johnson with this piece).
Not to worry, I made sure that the estate of Congressman Stephens provided me with a letter of provenance with each of the owners identified (including me as the current owner).
Note the date on the letter (first date of issue Kennedy half dollar) and the text (among the first). Not to mention President Johnson's signature on a White House letter!
Not shown is the letter of provenance and White House envelope.