Had a recent flight on LY to Dubai, and then had a separate ticket on CX to Hong Kong and Tokyo. At checkin for El Al i showed them my Cathay ticket and asked if they could interline the suitcase to Cathay all the way thru to Tokyo. Luckily this was a trainee at checkin with an experienced person there to teach her, so she was happy to jump in and show the trainee how to do this unusual checkin of the luggage. After some 10 minutes of typing, the luggage tags to NRT were attached to my baggage, and i did receive them when we landed in Tokyo.
So kudos to El Al for doing this (some airlines will not do interline of separate tickets at all).