bcdedit or EasyBCD ?
I guess they both make the same assumption, but I can't speak for MS.
EasyBCD assumes that the BCD will be on the "active" partition of the 1st HDD in the BIOS boot sequence.
If it isn't, (mine isn't) it prompts you for the location.
The navigation to it uses a standard Explorer dialogue box, which therefore needs the partition to have a letter.
(If the unlettered partition is "active", EasyBCD (and presumably bcdedit) will find it anyway)