CV Joint experience

LHS tends to wear first as our left hand turns are typically sharper than our right hand turns and the inside wheel turns sharper than the outside.

One other thing to consider is that the LHS is also subject to more potholes and other roadside irregularities than the RHS (usually high on the bitumen).

Agree with replace in pairs.

The knock you hear is caused by wearing through the hardened area of the joint, meaning the weaker "standard" steel is exposed to the pressure exerted by the balls (essentially point contact. As for how long it wiill last it would depend on weight of vehicle/terrain/Murphy's Law.

Change them now and carry both as spares (worn one would get you out of trouble if needed).

PS 200kms is normal for this sort of wear.