The guide uses the letters to indicate alternatives. That means 2A and 3A are one way to get to point 4, and 2B and 3B are another way. This becomes clear when you look at the map. Same for 10A and 10B, two very different ways to get from Guardo to Puente Almuhey. 12A and 12B are two different ways to get from Cistierna to Boñar. The one piece that may be confusing until you look at the map is how to get from point 13 to point 16. And that’s because the “A” version is two days (13A - Boñar to La Robla; 14A - La Robla to La Magdalena). The “B” version is three days (13 B - Boñar to Vegacevera, 14 B - Vegacervera to Buiza/Pola de Gordón; and 15B Buiza to La Magdalena). So there is no 15A stage at all.
The stages aren’t set in stone, of course, and you can adjust depending on accommodation and your ability, but 21 days to Ponferrada is pretty do-able, at least for the types of people who are drawn to the Olvidado.
Does this help?
And p.s., I would also look at Ender’s English Olvidado guide, which is very similar in format to his Salvador guide and maybe more straightforward.