I’ve been on Radio Jingles 24 and listened to their sample oldies jingle beds, most of them use the same vocals whereas the vocals in 3 of them sound Ken R-ish.
The jingle beds I’m talking about are jingle beds 18, 20 and 21. It is unknown if they are the Ken R singers or not.
I know a lot of the RJ24 Oldies jingles are resings of Ken R and Ben Freedman/CPMG tracks. It’s certainly possible that they kept some of the Ken R vocals.