When looking at stocks and taxes it says that you can direct which shares you want your broker to sell, but you have to be ready to prove that you chose those shares.
So in reality, even if you're doing FIFO or LIFO, if you want to choose a specific set of bitcoins to sell (older coins when you had been doing LIFO or newer coins when you had been doing FIFO) you can. As long as you prove that that is what you are doing.
So as long as every trade has a unique basis (including all future trades), the system is cohesive? Are timestamped spreadsheets good enough? as long as they include every account adjustment true to my 1099?