In almost every case I've ever seen of a drive B it's a partition windows creates to store its pristine CAD files or a partition created by an OEM to keep its factory original repair files. But B drive will be a partition on C drive. I've never seen an added drive get 'given' B as a drive spec, additional drives are lettered above C (plus optical reservation ), so usually start at E and go upwards. Drive A being reserved for floppy.
So the only way you'd get a 100Mb partition on that drive would be if it's a used drive that someone had as a boot drive for OS, replaced it and was smart enough to format both B and C, but not smart enough to bypass the boot partition lock.
Many people in returns departments would just check to see if anything was on it, and it'd come up empty, they'd not run a partition check or pay attention to the size of the partition or how many.
Just redo the partitions, do not reset it to B, use F as a single partition the size of the entire drive. Use GPT not MBR.