Belanger:
You stated:
"If 2009: use a flatness tolerance applied to (or under) the size dimension. If 1994/82: use a straightness tolerance applied to (or under) the size dimension."
If we are talking about a surface, I would not suggest that the flatness tolerance be placed under the size dimension. That could be construed as requiring the centre plane to be flat rather than the surface. Place the flatness requirement on the surface (leader or extension line) if that is the need.
The ASME Y14.5 2009 revision now allows flatness of the centre plane and also at MMC which is similar to straightness in the 94 standard. Rule #1 does not apply in such cases.
I would not suggest using straightness in your situation but if one did place it under the size, it would be the straightness of the axis rather than surface. I do believe that we are talking about a surface and not an axis in your case. Again, I would not suggest using straightness.
Rule #1 does apply if the concern is a surface rather than a plane or axis.
Lastly, all parts are confirmed in a free state (unless otherwise specified) and I do believe that the part in question would be relatively rigid and also be confirmed in a free state.If the part in question is a piece of jelly, then rule #1 does not apply.
The 2009 std., paragraph 2.7.2 (b) refers one to 5.5 which details the application of free state. The example here is a thin wall product where the wall flexes.
Just another point of view.
Dave D.