Still learning new things about MAS 90 after 20+ years. Relates to BOM Costed Bill of Materials Report (I apologize for the detail and wordiness so early in the morning).
If you use the Range of Bills Option (even if you only actually pick one Bill), regardless of Cost method you choose, it uses a rolled up calculated cost on all Subassembies in the Base Bill. However if the Bill has Options and you put a Subassembly item on an option (not supposed to, but system doesn't stop you), it does not do a roll up but instead uses your selected cost method when you chose when you ran the report, basically acting as if it were a component item. End result is that it is possible to have different costs for the same item on the same report. If you run the report using Specific Bills, it does not do any rollups on Subassemblies regardless of where they sit on the bill. So two oddities: 1)You can get two different costs on same item on same report and 2) running the same report (using different options) will give you two different results.