Anthropic, the company behind Claude, lost $80.7 billion in six months, according to its draft IPO filing. About $72 billion of that happened because the company got more valuable, and if its value had crashed instead, the same accounting rule would have booked it a gain on paper. That sounds made up, so here's how it works. When Anthropic raised money, a lot of it came in through convertible notes and similar deals. Think of them as IOUs that turn into stock later. Accounting rules make the…