Apparently some older H3500 units, around 1993, with manuals 
copyrighy statement of 1989-1992, have less presets then later H3500 
production:

This is a list of what some of those older units might have and miss

150-424 empty <<<<<<<<<<<<<<<<<<<<<
425-493 Percussion & Other Presets
496-499 empty <<<<<<<<<<<<<<<<<<<<<
500-534 Chorus/Flange/Thickeners
535-554 Delay Effects
555-574 Small/Ambient Reverbs
575-589 Large Reverbs
590-604 Alternative Reverbs
605-629 Pitch Shift Effects
630-674 Unique/Filter Effects
675-689 Tone Generator
690-699 MIDI Controlled Effects
700-747 empty <<<<<<<<<<<<<<<<<<<<<
750-786 Custom Presets
793-799 empty <<<<<<<<<<<<<<<<<<<<<
800-899 Mod Factory
975-999 empty <<<<<<<<<<<<<<<<<<<<<

In those years, Eventide had 3D spatialization presets and Steve Vai 
presets available on eproms, that could be added to these H3500.
Later units include ALL presets, so those specific eproms are no more 
available. Those presets are today included into D/SX (Vai) and D/SE 
(Vai + 3DSpatial) Conversion Kits.

A full presets list of later production units is available here:
http://www.eventide.com/profaud/3000pres.htm