Jack,

Check out IPC-2222 9.1.4 (published Feb. 1998)

It basicly states that nonfuntional lands should be included on
internal layers for all plated through holes -....
but greater than 10 layers, or where electrical requirements don't
permit, it is okay to remove some of them.... (my interpretation).
 I also recently took a class where they talked about leaving them,
but I can't remember what the reasoning was -but we did make
the change.
Lynn Isaacson
Medtronic Physio Control

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