I think the magnet sheet should have its own line in the BOM separate to the "Spring Steel Flex Buildplate 120x120mm (OPTIONAL)", especially given that the sourcing guide recommends buying a better quality sheet than the ones that can be bundled with the spring steel plate:
"base" refers to the magnet which is not very good, better to buy a stronger 3rd party one
I think the magnet sheet should have its own line in the BOM separate to the "Spring Steel Flex Buildplate 120x120mm (OPTIONAL)", especially given that the sourcing guide recommends buying a better quality sheet than the ones that can be bundled with the spring steel plate: