There can be an ebony as far back as 4+ generations and it show up ... that's why it is often referred to as a 'wild card' ... if there's not a known ebony in the background, it could be considered a "dirty belly" and, as Jamie said, sold as 'pet quality chinchilla, not for breeding' (unless mated with an ebony - depending on the other breeding qualities of the chin) .
With having other nice litters, I would keep them in breeding ... if the quality of the other kits is good ... I would let any future buyers know that there is a
slight chance/possibility there is an ebony in the line
somewhere and/or one standard was produced with a possible "dirty belly". To most folks that want a "pet" that would not matter, but to a breeder, it would.
Jo Ann