As with most computer systems, the Tool will give you exactly what you ask it for, no more, and no less. If you ask for a YOW-DEL fare, it will give you exactly that -- a YOW-DEL fare ($1150). All fares are filed by the respective airlines (or their authorized agents), and the Tool does not modify those fares in any way.
Also, there is no such thing as "a combinable fare [(singular)] closer to $650", series of combinable fares. If you "try to enter the segments manually" and request fares for YOW-BOS and BOS-DEL separately, then you will get exactly that.
Thanks, for the info.
What about my example of YOW-YYZ followed by YYZ-YVR? If the sabre access (or aircanada.ca) methods do not give me a particular combination of the 2 segments that I am interested in, would the combined fare (of the 2 segments) be equal to the single fare that is displayed for YOW-YVR?