Blueglasses, it appears the exam board is happy with the text and they have been running exams for more years than I suspect you've lived. Surely if there was such an error as you assert exists, then it would have been picked up at some point in the last seventeen years, and as Hildegard points out Butterworth and yourself appear to be in agreement about the 6-4 chord.
Perhaps if you were to provide the names of the texts that you deem to be superior, rather than mentioning that they exist it would be easier to compare them with Butterworth's approach.
Any exam board does not hold any monopoly in musical education be it teaching or performing and when it comes to the teaching of music theory, all the UK accredited exam boards fall so short of musical (sound to symbol approach) theory resources when it comes to aiding the UK learner. We are still offering texts that are so outdated and views that are NOT in line with international thought and parlance. The Butterworth text for one has received no revision since its publication in 1999 and that says it all. What is so needed in the UK is VISION to make music theory MUSICAL.
I am an ex music examiner so I have all the experience necessary to state what I have said. I note your musical credentials which are so basic so save your words for the novice! Oh YES! I can certainly provide the titles of texts that are far superior to the Butterworth text and feel free to come and see me at my studio in Northern Ireland and I can show them all to you as well as their ancillary resources such as Instructor Manuals etc which alone have more details than the measly offering by Butterworth at the time.
You most definitely need to research these texts as you will be blown away by the depth and musicality in these international resources.
I am smiling here as what seems to have been revealed is your lack of knowledge which I find very alarming.
Feel free to purchase the following (of which I have all of them!) read through them and then I dare you to get back to me and try remaining loyal to the Butterworth text!!!!!
1)Tonal Harmony-Kostka and Payne-5th / 6th / 7th Edition-McGraw Hill 2)The Complete Musician- 1st / 2nd / 3rd Edition-Steven Laitz-0UP 3)The Musician's Guide to Theory and Analysis- 1st / 2nd Edition-Clendinning and Marvin- Norton
4)Theory for Today's Musician-Ralph Turek-McGraw Hill 5)Harmony and Voice Leading-4th International Edition-Aldwell, Schachter and Cadwallader-Cengage, 6)Harmony in Context- 1st / 2nd Edition-Roig Francoli-McGraw Hill
I also highly recommend (before a study of tonal harmony begins) either of the following courses of which all are sonic orientated and deal with all aspects of fundamentals and beyond:
a)From Sound to Symbol by Michael Houlahan and Philip Tacka (text and ancillary resources), b)The Musician's Guide to Fundamentals by Jane Clendinning, Elizabeth Marvin and Joel Philips, (text and ancillary resources) c)Understanding the Fundamentals of Music by Robert Greenberg (dvd lecture course).
d)Explorations in Music by Joanne Haroutounian, published by Kjos
e)Sound Advice by Brenda Braaten and Crystal Wiksyk, published by Frederick Harris.
f)Theory Gymnastics by the "Three Cranky Women", published by Kjos - in my opinion these resources are the best of what's on offer throughout the world. Try them and you will NOT look back!!!!!!!
All of these courses offer a theoretical course of study in fundamentals and beyond with the philosophy that the sound works WITH the symbol and not WITHOUT it. Sadly, this is NOT what the UK accredited examination boards of music (ABRSM/Trinity Guildhall and LCMM) are offering in their graded examinations at this moment in time and the texts/workbooks of all the UK exam boards are so boring, unmusical and not of the same calibre in standard when it comes to the USA/international texts/workbooks.
The only accredited music external exams board to offer such an examination is by the Australian Music Examinations Board-AMEB.
Check out their Music Craft syllabus, it's the BEST!