Tractate Shabat page 69. Rambam accidental sacrifices 7:3 and the Avi Ezri on that Halacha [i.e. Rav Shach's book on the Rambam]
I doubt if I can explain this right. But here is at least a first attempt. The way I put this when i was learning with my learning partner was this: we have this idea of Reish Lakish that an accident is only when he forgets that some kind of work is forbidden on Shabat. And if he forgets all 39 types then he brings 39 sin offerings. The Talmud asked then in what way did he remember Shabat? And it answers the Sabbath boundary. The problem the Talmud is addressing is what makes this case any different from when he forgot the Sabbath day completely and then has to bring only one sin offering no matter how many acts of work he did. Now this is really the question of my learning partner but I am trying to put it in my own words. So the question is how has the Talmud answered anything? He knows Shabat but only in something that is not related to a sacrifice. Just the Shabat boundary.