Testing out this lead, it appears if a unit already has prepared, and gains it again, they do not get offense and crit damage up.
Example, Qi-ra will gain prepared when dash attacks and gets 2 crits. She gets the animation of gaining prepared, but no buffs. Likewise if you use young Lando or Han to pass prepared they unit they pass it to don't get those buffs.
So not quite as good as I first thought. The wording of the lead should be changed to show this. So it should be "If a unit is not prepared and they gain prepared then...". It may mean you can only ever gain those buffs once in GAC too, depending on how the lose it, gain it sequencing works.
Also L3-37 never gets those buffs, because her unique gives her prepared before Dash's lead kicks in.