If you have saver availability by segment (T for coach, U for business) but not for the itinerary origin-xxx-destination, you may have:
1. Connection times too long (and so a stopover, not a connection)
2. An invalid routing origin to destination
3. An example of married segment availability applied to awards
I believe one can dismiss #2 on the basis of this allowable routing from ExpertFlyer for an AA fare GRR-ANC.
MAP CONSTRUCTED LEFT TO RIGHT AND RIGHT TO LEFT
1. GRR-DFW/CHI-PHX/LAX-PHX/LAX-ANC
2. GRR-DFW/CHI-PHX/LAX-SEA/PDX-ANC