Originally Posted by
Ditto
Creating a PNR is one thing, ticketing it is a completely different thing where all the different restrictions comes into play.
Your answer is the key to this discussion.
It's not because flights are there and flight numbers, codeshare or otherwise exist, that you can just slap them on a ticket.
The concepts of Fares, Fare Rules and, in this discussion, ROUTING RULES, seems to be utterly unbeknown to some.