wfjm.w11/tools/oskit/xxdp_rl/README_license.md

Unlike most other PDP-11 software xxdp was not sold to Mentec. By now, ownership of xxdp software is in the hands of HP.

PDP-11 customers were not required to sign a license agreement for xxdp, the software was provided with the system or brought to the customer site by a Field Service representative.

Bottom line is that there is certainly a copyright on the xxdp software, but it seems that there is no license restricting the usage.