This is a subject of seemingly endless debate, with no one ever discussing the science involved. Pitching rates are guidelines not hard fast rules. They were also created from commercial breweries with regard to repitching yeast. I don't have my Yeast book with me but as I recall vitality is completely ignored. According to the yeast scientists, with doctorates in microbiology, you can pitch half as much fresh laboratory cultured yeast to get a quality fermentation. I have done it both ways and really the results are subjective and inconclusive IME. The most important thing is to be consistent( as possible as one can), but I have no idea how much yeast I pitched from a starter or a straight pack. There are very different numbers being thrown out there from calculators depending on which person you go with.
As far dry yeast and pitching rates go, that one is very difficult to ascertain. Safale 04 and 05 for example have >69 billion cells at packaging according to Fermentis. The liquid packs have about 100 billion. But the liquid is never enough and must be built up while the dry can just be sprinkled on without rehydrating ( which supposedly kills half the cells) Maybe someone here can help me with the math, cause I can't wrap my head around it.
Sorry for the lengthy first posts but I am excited to see there is a forum about making beer and have tons of questions and a thirst(bad pun?) for knowledge.