It should be noted that the so-called Classic Theme is NOT the same thing as what a layout looks like when first converted from pre-12.
To test, just take a previously-untouched-in-12 layout as converted from FP7, and then Change its Theme to Classic. Classic imposes a specific color scheme, etc.
This is important in light of the info that Classic Theme is the only layout theme compatible with IWP.
Also, if you apply any theme, you cannot get back to your original converted layout's settings by later changing back to Classic Theme, because Classic Theme is not where your converted layout really started.
Be sure to make copies of original layouts before applying any theme, even Classic.