Often you will run across a series of CRTs which had different inputs for different sizes or models of the same series. The manufacturer will exclude certain "premium" inputs from the back of the CRT but left the hardware inside the same. This means the hardware inside still supports adding those inputs if you do the wiring yourself. Sometimes its even easier if they left headers for the connectors to be added and did all the wiring for you!
The method will differ from every CRT and therefore a universal documentation can't really be made. If you see a Composite or Video input on your Chroma Chip in the CRT schematics, your TV supports Composite input. From that point you just need to order a female RCA connector from Mouser and run the wiring yourself.
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