Booktype only applies to DVD+R(W).
Booktype is meant to increase disc compatibility and allow the discs to be seen as DVD-Roms, and it can be of any use for some topset devices, but the importance is much lower than it used to be.
You can do it using the bitsetting facility if your burner or/and recording software supports the facility.
NEC 3550A original software only supports bitsetting for dual layer discs, but you ref your version is 1.6y and this seems more like a modified version, not the original.
If that's the case, it shall support the facility for DVD+R and DVD+RW also, as you can see at the authors link (Liggy's and Dee's modified NEC firmwares):
Is it that?