Hi Darren.
Good question - there seems to be a bit of confusion over this.
Here is my take on it (may be wrong).
Guro = Teacher
Bihasang Guro = "skilled, fluent, used to, accustomed to" Teacher
Punong - Guro = Principal Teacher (like a headmaster).
Dalubhasang Guro = Expert Teacher. Awarded to those who teach (or have the ability to teach) other teachers or
whose students become teachers.
Master - Self-explanatory.
Dakilang-Guro = Great Teacher / Founder.
This is from memory and with the use of
http://tagaloglang.com - a good site there.
As you can see from above, there is a lot of overlap between the distinctions. There is not a lot of difference between the definition of Punong Guro and "Dalubhasang Guro", it just depends whose using it and how

Those that know GM Yuli will know that he does not put that much precedence on rank. In his words it's always:
"What you can do in front of him" and "You must carry the art!" (i.e "Prove it!").
He also says "There are no seniors in sparring". I take that to mean again that the stick will show you who's who and won't be stopped by titles but by skill alone. "Bahad Zu'bu" - the threat of stick and knife.
I do however think titles are very important for those who are overseas teaching and outside our art.
I remember being back at Seni 08 in London. Somebody asked me about my Master. He asked "What Dan is he?". I related the story to GM Yuli and we had a good laugh....
Hope this helps,
Simon.