You're asking a NetBSD operational question in an OpenBSD thread.
On OpenBSD, if there is no OpenBSD disklabel on a drive with an MBR, any recognized MBR partitions are assigned
virtual partition letters starting with "i". This has nothing to do with NetBSD, Windows, or any other OS. This has only to do with recognized foreign partition types in an MBR partition table.
Those virtual disklabel entries may become physical disklabel entries if an OpenBSD disklabel is written.