If you buy the ticket from travel agent, they can supply you 2 record locators.
1) The PNR that you can check on the website. Like checkmytrip.com etc...
2) The CX PNR, which is the one that some of you said before, the 5 digit PNR.
But, these 2 record locators are linked together. The 6 digit PNR is the real PNR. The CX one act as the reference number for CX only.
If you ask your travel agent, they CAN give you BOTH. So, even for CX flights, you CAN check on net!!!