Compression Ratio increase

[PDoane]

The rules say

Where a factory specification for original cylinder head thickness
can be proven, a tolerance of .025 inch less than the
service limit will be permitted. Under no circumstances may
the compression ratio be increased by more than one-half
(.5) point. An offset key may be used to return cam timing
to the factory specifications. On engines with dual overhead
camshafts, this key shall be installed on the crankshaft only.

Since it says that right after the line about head thickness and before the line about offset key, I would assume you gain the CR by milling the head, but it doesn't say you have to. Milling the block or CR increasing pistons are other options.

Would a CR increasing piston violate the piston rule?

Engines may be bored to a maximum of .040 inch over standard
bore size. Factory replacement pistons or their equivalent
with the exception of diameter shall be used. Cast or forged
equivalent pistons shall provide the same dome/dish/valve relief
configuration, ring groove width and spacing, pin height relationship,
weigh no less than the factory standard bore pistons.
Piston rings are unrestricted.

Thanks for any info/help

Peter