You can connect the ground plates to one service enclosure and then jumper to the second enclosure. Here's a breakdown of why and how

Understanding the Requirements (NEC focus):
Grounding Electrode System (GES)

Your ground plates are part of your GES.

Connecting to the GES

The NEC requires you to connect your service equipment (the meter/main enclosures) to the GES. This is achieved through the Grounding Electrode Conductor (GEC).

Bonding

Bonding ensures that all metallic parts that are likely to become energized are connected to the grounding system, providing a low-impedance path for fault current.

Continuity

The grounding system must be electrically continuous.

Applying it to Your Scenario

You can do this in a way that follows the NEC with a properly sized GEC.1. From Ground Plates

Run

one continuous #6 AWG stranded copper conductor from the ground plates (your grounding electrode system) to one of the service enclosures (doesn't matter which one).2. First Enclosure Connection

Connect this #6 AWG GEC to the grounding bus or terminal bar within the first service enclosure. This enclosure becomes properly grounded.3.

Jumper (Bonding Jumper)

Use a

#6 AWG stranded copper conductor to jumper (bond) from the grounding bus/terminal bar in the first enclosure to the grounding bus/terminal bar in the second enclosure.

Important Considerations



Continuous

The GEC (the one running from the ground plates to the first enclosure) MUST be continuous. You can't splice it along the way.

Proper Connections

Use listed connectors or compression lugs appropriate for the conductor size and the type of enclosure/grounding bus you are connecting to. Make sure the connections are clean and tight.

Material

Use copper for the GEC and bonding jumper.

Exception

If you have metallic water pipe that is part of the GES, then you will need a separate GEC to it, and the ground plate(s) may not need to be connected to both services, unless they're the only electrodes you have.

Important Considerations



Local Codes

Always consult and comply with your local electrical codes and regulations. They may have amendments or specific requirements that differ from the NEC.

Inspection

This work should be inspected by a qualified electrical inspector.

In summary, one #6 AWG to the first enclosure, then a #6 AWG jumper to the second is the standard, permitted, and often preferred method. Flag for review