I have a font that I have installed on my system (Mac OS). The font has a glyph that I can see in FontBook but does not show up in Glyph Designer. The designer on the project says the glyph is a "secondary" glyph and I know the unicode code for it.
In FontBook the character is reported as glyph 73 but in Glyph Designer that glyph is something else:
and here is the fontbook snap (the tooltip is hard to read)