Gary,

	The 1 oz for 2 oz swap can be less than totally safe.

	The major differences, thickness and power handling, can manifest
	themselves in a couple of ways.

	If a large board contains many high-powered devices the 2 oz's may
	be needed to minimize plane impedance (voltage drop).  The same
	thing applies to any board that supplies or passes-through power
	to a plug-in.  Similarly, 2 oz`s can be a band aid for a design
	that has improper combinations of anti-pad size and via-to-via
	spacings (inadequate webs).

	In some rare cases, we've needed to use 2 oz copper to make up
	thickness on difficult/critical impedance stackups, usually in a
	trade-off against standard material thicknesses and narrow windows
	for line widths.

	On the other hand, a great many part numbers (primarily in the 80's)
	were specified with a "rubber stamp" for 2 oz copper, and this may
	still happen today.

	Good luck figuring out which case your looking at!

	Jeff Seeger
	Applied CAD