Dear Basil:
Although I don't have the precise and measurable answers to the questions, I will offer my insight from many years of experience and discussions with people from Karamanis, Syrkas, Hatzimarkos, Sourlantzis and Vasilios Nikolaidis.
But still I think that at the time of the Three teachers only one style of singing was agreed in Constantinople.
That does not appear to be the case. Comparing the theoretical manuals and the historic accounts of chant in Constantinople, there were a number of styles that were ecclesiastically acceptable with minor variations in interpretations of the neumes and the cadences (theseis, ateleis and enteleis katalixeis as they are referred to in Greek). What the Chrysanthine System did was to provide a framework for TEACHING the fundamentals of ecclesiastical chant, offering the skeleton and some common practices shared by the different "schools" and then leaving it up to the individual teachers to offer the ornamentation. Ornamentation differed based on the vocal capacity of the teachers. Some were perfectly crisp in execution of a multi-gorgon, others less so. Others were perfectly smooth in "wavy" accentuation of a neume, others less so. And so on. Nonetheless, the general framework of the qualitative neumes was accepted by all.
Maybe the reason the explanations of the old teachers were vague was that it was simply impossible to explain with words the meaning for the sings. For example what non-vague explatation can be used for the ornaments in this or in this piese?
I listended to the two pieces. If I had about an hour, I could have made a rough transcription of them (although orthographically I would not be following the rules completely and people like Fr. Ephraim would be sought to correct my orthography). But the two pieces, feature a person who does not have the crisp capacity to execute a trigorgon on an yporrow for example. Also, in certain parts, the series of apostrophoi are performed in a portamento manner instead of discrete specific descents. And so on. This is what we term "improvisation" although the improvisation is perfectly in line with tradition. That is why it is my view that a bounded and limited and fixed dogma of formulaic expression is not in the spirit of classical ecclesiastic chant. The formulae can be used as a skeleton and a framework but they cannot offer the inspiration of the moment that classic psaltae performed and continue to perform.
The reason I think that there was one common interpretation of the qualitative signs is the existence of very complex system of orthography rules. For example only in ByzOrthography.pdf there are 106 rules! How were the Three teachers and their immediate pupils able to follow these rules if these rules were not systematized and maybe even unknown at that time?
The "rules" were the skeleton, or the scaffold. Practice and lots of listening were part of the learning process and indeed, most students at the analogion were not even offered books to follow. Consider the tradition at the Patriarchate. With the exception of a few hymns, chanting is from memory. The domestikos listens intently for many years, studies the books at home, BUT, at the analogion, he follows the Protopsaltis or the Lampadarios. The same was true for almost all churches in Asia Minor. Listening was critical. Execution and interpretation was passed on ORALLY and not formulaicly.
Why didn't the latter composers/publishers follow these rules as strictly?
Vide Supra
My answer is that in the latter time the ornamentation has changed so many of the qualitative signs lost their original meaning.
Not true. If you have a month to spare, go to the audio archives of the Institute of Byzantine Musicology of the Church of Greece. Take out audio material from the 40s and 50s and compare the THESEIS, the ATELEIS AND ENTELEIS KATALIXEIS and the interpretations of specific neumes of a few common hymns. You will see a remarkable adherence to a common "core" interpretation. The variations in the "edges" on the interpretations are small.
Consider for example the following:
1. Why vareia requires the next note to continue the same syllable?
Accentuation is difficult if you invoke a breath action (repetition of a syllable, especially a vowel) CONCURRENT with a tongue action (new syllable. Practical stuff.
2. Why is aple used instead of klasma for the next note after a vareia if this note is lengthened?
3. Why is aple used instead of klasma for the note immediately before the vareia?
I don't have an answer to these two questions and I doubt anyone has a serious one based on solid history. None of the people I spoke to has an answer.
According to Chrisantos during the klasma the voice "waives so to say" (§120) and here this "waiving" is interpreted as "punctuating" the note to measure the time/chronos.
I'm not sure obvious punctuation is the meaning. Certainly both the klasma and the apli (dipli, tripli) have qualitative activities that ask us to barely noticeably "wave" the extra additions of time, but they are not punctuated.
Consider, in general, that the THEORY of Orthodox Ecclesiastic Music came centuries AFTER an ORAL tradition. Much cannot explain the oral practices and at those times where there is no rational answer, we have to respect what generations of traditional psaltae have passed to us.
