When VH went to EBMM to have his sig guitar built he wanted to have seymour do the pu's but EBMM had dealings/agreement with dimarzio. so they went with dimarzio for the mass producer of the pu's.
The duncans that were shelved are called "black backs" .these are the prototypes seymour made for the EBMM EVH sig guitar. and you can still buy these for $130 each from duncans custom shop or ed roman
Anyway according to blucher many bridge p'u prototypes were made for EVH and he narrowed it down to 2 models ,one went on to become the tone zone and the other wound up known as the ebmm EVH bridge pu.(also called the axis bridge pu). and are in that guitar to this day.
this pickups starting point was the duncan JB in VH's kramer 5150 guitar.
This JB was not your typical off the shelf duncan JB model you can buy, it is the old school JB that uses a rough cast UOA5 magnet in place of the polished A5.(if you know anything about magnets and the effect on tone you will know that the two sound very different) So they used this pu as the template for the bridge pu in the EVH or axis.
this is why the spec's of the dmarzio EVH or axis bridge pu is so similar to a JB(16.5K alnico 5 wound with awg 44 and matched coils) essentially it is dimarzio version of a JB as is newly released the AT-1.
Get a JB and slap a roughcast UOA5 magnet it it and hear the JB in a new light! very VH sounding!
here is blucher talking about tone zone and EVH
IHG: With regard to when you said pickups don't exist in a vacuum, I imagine you seek feedback from various players from different genres when designing a new pickup? For example, Paul Gilbert was featured in an ad for the Tone Zone - did he have any feedback into its development?
Blucher: We sometimes seek opinions from players in different genres, but not when a pickup is being designed for a specific player or style of music. Paul Gilbert didn't provide any input towards the development of the Tone Zone. The only player who did was Eddie Van Halen, in the course of doing the pickups for the MusicMan EVH guitar. My understanding is that the final choice for the bridge pickup was between the TZ and the pickup he actually chose, and it almost literally came down to a coin toss.