Throughput Accounting.

Dear John, How are you? I hope you are doing well, I have a question in regards to Total factory costs under throughput Accounting according to opentuition note it equals to all production costs except materials based on what's mentioned my question is why do we exclude the material cost of production cost? 2nd question, According to my knowledge total factory costs, total production costs and total manufacturing costs all are the same is that right? Thank you in advance.