Yes, as you say, it is a historical forgery, so fundamentally it is a comparative analysis between the quartets of op. 18...
I have already performed in-depth analyses of Haydn and Mozart quartets (Haydn's op. 33 and op. 74), but with op. 18 I found myself facing something more complex, even if it is the "first Beethoven," obviously influenced by classical composers.
More than anything, I am trying to understand which compositional processes Beethoven put into action to "arrive" at each formal section, therefore the procedures for developing the initial thematic material. I noticed a particular detail: while in Bach, Haydn, Mozart, and Clementi one often finds oneself facing the so-called "Grundgestalt," i.e., the continuous development of an initial cell that is manipulated and subjected to conventional contrapuntal techniques, such as inversion and retrograde, in Beethoven these techniques continue to exist but in a completely different form! In op. 18 no. 3 in D Major, for example, the initial theme does not present a generating cell/motif that is then developed (as happens instead in the 5th Symphony) but a cantabile melody in the first violin, changing in its surface structure... I thus tried to look for what is commonly defined in Bachian melodism as "virtual" or "hidden" counterpoint and I identified two melodic lines, both ending with a whole-tone turning note (upper melodic line) and a semitone turning note mi# fa# (lower melodic line, tail of the thematic phrase)... immediately after a long subdominant in the second phrase reveals an arpeggiated substructure of E minor, then embellished with many semitone turning notes.
Coincidentally, the second theme begins with a semitone turning note and continues with a whole-tone turning note and an A major arpeggio, practically the "retrograde" of the first theme... but not at the level of notes, as in strict counterpoint, rather at the level of intervallic relationships; the content, rhythm, articulation, phrasing, duration, and phraseological structure are contrasting!
This makes me think that Beethoven no longer acts at the level of simple motifs as his predecessors did, but that he sought to develop musical figures that contrast with each other yet at a deep level, united coherently through the use of very simple and I would dare say "skeletal" melodic and intervallic structures, such as turning notes and arpeggios.
Now, this can certainly help me, but what I meant by "elastic method" is the agility of writing in imitation: I know well that it is the "Beethoven Cage circumscribed to 1797/1800," but within this cage I cannot shamelessly copy from the op. 18 quartets and do a copy-paste; I must achieve precisely that writing elasticity whereby I am able to write directly in Beethoven's style any type of phrase, from the theme's consequence to the modulating bridge, to the second theme, to the end codas of the exposition, to the development.... so almost "empathizing" with him, otherwise it would result in simply copying something already existing without possessing its real contents...