I do not always know if I have flown a B737-600 or B737-700 and hence will enter it as B737 (or Boeing 737) in the system. Next time I might know the series and will then enter B737-600 as type.
When looking at statistics I will from the above example see that I have flown B737 once and B737-600 once. I would like it to say that I have flown B737 twice (and perhaps you could click a + sign to get an expanded list with series?). The same applies to entering Boeing or just B, they ought to be grouped together.
I understand this would require a lot of work from the creator to create lists of manufacturer, model, series etc. So instead it could perhaps be user created? When entering aircraft type a menu would come up with available aircraft types. If not listed the user could simple add it and to what family it belongs.