Installing Pergo Flooring Question?

Why not install the sheeting anyway, just for GP (general practice). It certainly wouldn't hurt and it's not expensive. You can also get a thin foam sheeting that you cut roll out, cut to shape, and tape together with packing tape to make bigger sizes as an underlayment. This provides a moisture barrier, sound dampening, and a slight bit of give to make it less fatiguing to stand on the floor for a long time. They installed this when I had laminate put into my kitchen several years ago. It was amazing how much of a difference it made from the standpoint of leg and foot fatigue when standing in the kitchen for a long time. And, that was on a wood sub floor over a foundation, not a slab.