I always ask myself similar questions but I have resigned to the fact that, as above, Look at the race results, Pedigrees can help aswell as previous owners knowledge of their birds but at the end of the day you gotta race them.
Some long to short pairs may produce great middle birds, another long to short pairing in a different loft may produce slightly harder sprint birds or softer but faster long birds.
One thing we can be sure of when breeding pigeons is, they will throw all sorts and one has to learn their birds strengths and weaknesses and then try and produce birds with more strengths and less weaknesses. Easier said than done.
Also, we all have different ideas, preferences, visual characteristics and behavioural characteristics that we breed or select for so IMO no matter what the strain, if one breeder has established their own family based on a particular strain it will be slightly different to their mates birds of for arguments sake, the same origin.
For me, the best way to determine the type of bird is through its physical attributes, as some birds have short wings (w/c cannot fly long distance), big body (too heavy to fly long distance), too small of a body, etc...I don't really believe it when they say a bird is a sprinter or a middle to long distance bird if they do not meet the criteria mentioned earlier. Actually there is a video in Youtube that explains how to determine if a bird is such...just type "how to determine or know if a racing pigeon is a short, middle or a long distance bird"...hope this helps!