Here’s a little brain teaser….buried in the midst of a load of LPs I recently bought was a clear virgin vinyl LP in a plain white jacket. The odd thing about it is there are grooves cut both sides with nothing on them. The dead wax on side one has inscribed NITTY GRITTY and BP 360 LP1 along with NW RTI 19724. Side two dead wax has 13875 and BP 000. Any ideas what this is and what it was for….we’d be interested to find out.