My understanding is that the total material cost will vary for different MR credits as some credits allow you to exclude the cost replacement of reused materials.
MRc4 Recycled Content = Use the total material material cost + division 12 (Reused replacement costs are left out)
MRc5 Regional Materials = Use the total material costs + division 12 + reused material replacement cost
MRc6 Rapidly Renewable Materials = Use the total material costs + divison 12 + reused material replacement cost
MRc7: Certified Wood = Only total new wood costs.
Does this make sense?