When using VC B&W papaers, if you change the time and if there is any reciprocity failure, you can "create" a bump in the mid tones that changes the contrast as a function of size, right where you do not want problems. So, this potential problem is to be found in B&W as well as color.

The problem is more evident today in economy priced papers which do not have the sophisticated emulsions that the high end papers have.

PE