Missling can not assume a trial success in predicting cash flow and cash reserves. He has to assume the current run rate adjusted for any planned changes such as more or fewer trials.
If he said we have 6 months cash because we expect to have a drug on the market by then, everyone would be all over him. Legitimately so I think. They would be saying the company is in a financially precarious position and ripe for a forced takeover.
Saying the company has 2 years plus of cash reserves signals good financial condition for the company. I think investors find that reassuring. It also communicates to any potential partners or licensees a position of strength and reliability.
Do you remember the posts slamming Missling when the 10K or 10Q came out and said only 18 months of cash?