ok, check it out. it's pretty easy. When EQ first came out bard haste was supposed to stack. but, what ended up happening is that the hastes from the other hasting classes would supercede ours. But, our stat bonuses that the songs give would filter through. Kinda like wearing a Custom Cowl of Mortality and a pair of Silver Chitin Handwraps. You'll get the bonus stats but, only the greater haste will go through. Now with the advent of Luclin there are three different kind of song hastes. Bards were finally granted songs that were made specifically to stack with other types of hastes.

Such as Melody of Ervaj
http://eq.crgaming.com/spells/spelldescriptions.asp?Id=1462
which is type 2 haste. It stacks with all bard hastes. Then you have type 3
Which is seen in Battle Cry of the Vah Shir
http://eq.crgaming.com/spells/spelldescriptions.asp?Id=1793
which was specifically made to stack with other kinds of haste. Now I'm not sure whether or not Melody of Ervaj Stacks with BCoVS as well as say Celerity which would mean a 20% increase in haste. That clear things up for you?