Oh yes, the "slavers"(he could have been adopted straight out and the pre-rebellion part doesn't change at all, and it wouldn't have been as simple as "hurr we stole your slave crest, so we own you, now do what we say!" leading to the Basam family being killed) that gave him a proper education, taught him magic, eventually adopted him into their family, gave him gold to start a little nest egg for when he is freed so as he doesn't become homeless and gave him a place to belong. His status as a slave is mentioned literally 3 times before the rebellion(once at the auction, once when he is told when he will be released, and when he is told he is to become a Barrier Master at the Royal Palace(where they talk about his release from Slavery in order to accept the role). The slavery(and subsequent slave seal) were a shitty plot point that existed just to kill off Lynos' family and enrage him enough to wipe the Rebels completely off the map(including the Royal Castle!) so he wouldn't be restricted from traveling due to having nothing and no one left in that Kingdom. He legitimately lived a better life in the 8 years he spent with the Basam family than 99% of the setting will in their entire lives, slaves or otherwise. Hell Lynos was treated so well by the Basam family even HE forgot he was a damn slave(well until the Rebellion anyway), lol.