Assuming the screens are otherwise the identical, and the only difference is the shiny glass panel on the glossy screens (this is a big assumption: I don't know whether it's true), then:
As a simple matter of physics, the AG screens would have to be at least a little brighter than the glossy screens. The light transmitted by the glossy screens has to be transmitted through 1 more optical element than the light transmitted by the AG screens must pass through. One more piece of glass to transmit through means more light reflecting back on the inner side, more scatter, diffusion, distortion, filtration, etc. No glass is 100% optically perfect. The fact that you can see the glass the fact that it's not invisible demonstrates that it is having an effect on the light. Passing the light through one more piece of glass would have to decrease the output by at least some small amount.