Well, spank me courageous... searching for ZM1...

MULTIPROTOCOL ADAPTER FRU P/N90X8995 (OPTION #6451003) REPLACES
FRU P/N72X8530 (OPTION #6450348). FRU P/N90X8995 IS SUPPORTED IN
THE FOLLOWING MACHINE TYPE/MODELS.

Note: There is a new level FRU ( P/N85F0004 ) now available that
has in turn replaced P/N90X8995.

8550-A00 8550-B00 8550-C00 8550-021 8550-031 8550-061
8550-900 8560-041 8560-071 8580-041 8580-071 8580-111
8580-311 8570-E61 8570-121 8570-A21 8573-061 8573-121
8555 - 031 8555-061 8565-061 8565-121 8590-XXX 8595-XXX

CAUTION:

OLD LEVEL MULTIPROTOCOL ADAPTER FRU P/N72X8530 (OPTION #6450348)
IS STILL SUPPORTED IN THE 8550-021, 8560-041, 8560-071, 8580-041
AND 8580-071.
OLD LEVEL CARDS MAY DISPLAY ERROR CODE 10062 OR INTERMITTENT
ERROR CODES 10029, 10030, AND 10031 IF INSTALLED IN ANY OF THE
REMAINING MACHINE TYPE/MODELS LISTED ABOVE THIS CAUTION.

THE NEW LEVEL CARD IS DOWNWARD COMPATIBLE (CAN BE USED ON ALL
MODELS) AND WILL BE SUBSTITUTED IF AN OLD LEVEL CARD IS ORDERED.

HOW TO IDENTIFY THE TWO ADAPTER CARDS:

1. RAW CARD ASSEMBLY P/N6278226 OR P/N72X6821 ARE USED ON
THE DOWN LEVEL ADAPTER. RAW CARD ASSEMBLY P/N90X8459 IS USED
ON THE NEW ADAPTER. (RAW CARD PART NUMBER IS LOCATED NEAR THE
CARD RETAINER).
2. NO COMPONENT IS INSTALLED AT LOCATION ZM1 ON THE DOWN LEVEL
ADAPTER (ZM1 IS LOCATED ON THE UPPER RIGHT HAND CORNER OF
THE ADAPTER). THERE IS A COMPONENT INSTALLED AT LOCATION ZM1 ON
THE NEW ADAPTER.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

It might be the old and newer are downlevel?

MULTIPROTOCOL ADAPTER
FRU P/N90X8995 (OPTION #6451003) REPLACES FRU P/N72X8530 (OPTION #6450348).

FRU ( P/N85F0004 ) has replaced P/N90X8995.

So...
Old FRU P/N72X8530 (OPTION #6450348)
Newer FRU P/N90X8995 (OPTION #6451003)
Newest FRU ( P/N85F0004 )

OLD LEVEL MULTIPROTOCOL ADAPTER FRU P/N72X8530 (OPTION #6450348)

STILL SUPPORTED IN 8550-021, 8560-041, 8560-071, 8580-041 AND 8580-071.

OLD LEVEL CARDS MAY DISPLAY ERROR CODE 10062 OR INTERMITTENT ERROR CODES
10029, 10030,
AND 10031 IF INSTALLED IN ANY OF THE REMAINING MACHINE TYPE/MODELS
LISTED ABOVE THIS CAUTION.

THE NEW LEVEL CARD IS DOWNWARD COMPATIBLE (CAN BE USED ON ALL MODELS)
AND WILL BE SUBSTITUTED IF AN OLD LEVEL CARD IS ORDERED.

HOW TO IDENTIFY THE TWO ADAPTER CARDS:

Old RAW CARD ASSEMBLY P/N6278226 OR P/N72X6821 ARE USED ON DOWN LEVEL
ADAPTER.

New / Newest
  RAW CARD ASSEMBLY P/N90X8459 IS USED ON THE NEW ADAPTER.

(RAW CARD PART NUMBER IS LOCATED NEAR THE CARD RETAINER).

Down level
Downlevel -
No ZM1

Newest - ZM1

(ZM1 IS LOCATED ON THE UPPER RIGHT HAND CORNER OF THE ADAPTER)

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

Downlevel

Old FRU P/N72X8530 (OPTION #6450348)
Newer FRU P/N90X8995 (OPTION #6451003)

New Level
FRU ( P/N85F0004 )
FRU P/N96F9156 replaces P/N85F0004, rework is possible...

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

https://fccid.io/ANO9SA6450348

The last version still uses the same FCCID as used by the earliest MPCA.

1987-03-31, but no further info.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)