That's precisely the point.
Yes, a roman coin was made by a slave, therefore it was made by a slave. it doesn't end.
If a company was upstarted with slave labour, it doesn't matter how many years since they stopped the practice, they were still upstarted by slave labour and cannot simply wash their hands of it because time had passed.
When someone is enslaved a horrible imbalance is inflicted upon the society involved, and the repercussions of that do not automatically re-adjust. All the effort that went into maintaining someones subjectivity, into destroying their spirit of rebellion, into breaking down and limiting their self confidence- a shit ton of effort was put into that. It wasn't just whips and branding, it was a psychological game, and that game was embedded into their daily routine and culture. That entire society began to change and adjust to reflect that imbalance, to maintain that slave-master relationship.
Unless the exact same effort is put into re-establishing the balance, into destroying the master-slave cultural connotation...unless that happens, the imbalance remains, and the effects of slavery continue to be felt....generations can pass, and it will still be felt and remembered. It will not go away. UNLESS that same blood and sweat and time and effort is put into establishing a culture of respect and brother/sisterhood, as it should be.