Wildbow did start out with a buffer of prewritten chapters. I think when he started he had arc 1 written, and arc 2 mostly written. However he ended up burning through the buffer pretty quickly. He used up the last of it some time during arc 6 or 7. Since then, most his chapters were written the day they were posted. Despite this, he’s manged to go 6.5 years without ever missing one of his regular Tue/Sat updates.
Damn.
No wonder he had some choice words about my early schedule. This is clearly a guy who’s good at sticking to his own while still producing high-quality content.