Not that it matters, or can be proved either way, but do you think they actually ever traded in anything?

There seem to be two basic ponzi models

1) Ones which are, from the get go, pure scams pretending to trade but solely designed to gain credibility and deposits until such a time as the admin take the money and run

2) Ones which start off as legit investments and 'go bad'. They have a core business which is real but unexceptional, which is then developed on by the owner for reasons of greed and hubris and becomes a ponzi. If you believe anything that Madoff says, for the first thirty years he was straight.

Hindsight is a great thing, but I followed BT quite carefully and came close to a dabble, luckily deciding not to.
The decider for me was I didn't believe that John Carley existed, there were too many inconsistencies in the story.
If he didn't/doesn't exist then I think BT must go in category 1.