I did a little reading about the two defensive backs they claimed.
In the summer of 2017 Chris Jones tore his meniscus which meant that he only played four games as a senior last season. Before the injury he had a reputation as a lockdown cornerback, and he was considered a mid-round draft pick. He is a physical press man-cornerback which suits Al Holcomb’s defense well.
Most think that the injury, and the fact that he rushed back from it and in doing so played sub-par the rest of the season, caused him to go undrafted.
With the Lions he impressed in their training camp and preseason games. Obviously not enough to make them want to keep him, but supposedly it was basically because he fell victim to a number’s game at cornerback, and as far as I can tell, they wanted him back on their practice squad.
Demetrious Cox had a very strong junior season at Michigan State, and many analysts thought he would have been a high draft pick if he came out after that year (it was reported that at least some scouts had a first round grade on him). He didn’t, his senior season went south, and he ended up going undrafted.
Cox was the leader of Michigan State’s secondary, and, by the way, remember that such things says something when you have Mark Dantonio as your head coach, and Cox has played both safety and cornerback in college.
Steve Wilks was the defensive coordinator with the Panthers when they claimed him off waivers last season, and thus probably were involved in the decision.
Both players are said to be great special teams players.