MEMORY ADAPTER (#6074): Permits the addition of up to 3Mb of memory.
   The first 512Kb increment of memory is included with this adapter and five 512Kb Memory Expansions (#6075) can be added, for a total of 3Mb of additional memory.

    This adapter comes with the first 512KB installed. You can add 5 more banks of 512KB each for a maximum of 3MB.

  Memory is added in the order Bank 1, 2, 3, 4, and 5.

SW1 Settings for Installed Memory Amounts
Bank x        1    2   3    4
 0  (512K)   Off  On   On   On
 1  (1MB)    On   Off  On   On
 2  (1.5MB)  Off  Off  On   On
 3  (2MB)    On   On   Off  On
 4  (2.5MB)  Off  On   Off  On
 5  (3MB)    On   Off  Off  On

Memory Expansion Installation 
    IBM 7552 Industrial Computer, Installation and Operation Guide (P/N 85X2023) pg. 3-44
   "The memory expansion adapter includes 512Kb of memory already installed. The first memory expansion adapter installed in the system unit will fill the memory to the maximum 640Kb that is addressable by DOS. The additional memory goes above 1MB and can be used by OS/2 . On each of the remaining four memory expansion adapters that can be installed, the system addresses all 512Kb of memory to give a total of 3MB of memory when five memory module kits are installed on the memory expansion adapters.
   If you are adding more than 512KB of memory to a memory expansion adapter, you will need to install the additional memory modules to the memory expansion adapter before installing the adapter in a shroud. The first memory expansion adapter will hold a total of 2.5MB of memory with up to five memory modules of 512KB each installed. The second through the fifth memory expansion adapters will hold a total of 3MB of memory each with up to five memory module kits of 512KB each installed."

   OK, like what does the last paragraph mean? Do the math, possible five memory adapters of 3MB each is 15MB, Add the 512KB on the Processor Card, and you are still below 16MB.