Yes, back then (2005) I didn't know about ABC nor Lilypond (which I've started using since end of 2011, month after end of my music prototyping Ask HN thing: https://news.ycombinator.com/item?id=3089259, which will hopefully get some follow-up in the future).

To be honest, today I would slightly change my notation, to make it more readable, consistent and friendlier for English-speaking people:

  OTD[.]
  O - octave: [0-9]
  T - tone: C,d(es),D,e(s),E,F,g(es),G,a(s),A,b(es),B,P(ause)
  D - duration: [0-9A-Z] meaning:
                breve (double whole note) // for D==0
                1/D note                  // for D!=0
  . - dotted note, changes duration to:   // d - duration
                d(2 - 1/2^n)              // n - number of dots

Same fugue would start like:

  4A8 4G8 4A8 4F8 4A8 4E8 4A8 4D8 4A8 4d8 4A8 4D8 4A8

which is so much more better...

Why I didn't do it like that from the beginning? No idea...