HP 4 FAMILY - Manual (Page 105)

Limitations The following limitations apply to Format 16 Font Headers
for bitmap fonts:
The Font Type field for Format 16 bitmap fonts must be
set to 3. This is the case for 1-byte as well as 2-byte
bitmap fonts. First Code and Last Code fields need to be
set.
Format 16 optional data segments are ignored for bitmap
fonts. These include the galley character segment,
vertical substitution character segment, typeface string
segment, and vertical rotation segment.
Vertical rotated printing (character text path direction
command, ?&c-1T) is not available for bitmap fonts.
Printer-Specific Differences 2-69