Note that the groove at the top of the Slide Lock engages a similar groove on the bottom front of the barrel lug. If the Slide Lock's groove is facing forward, the barrel lug's groove can never fit into the Slide Lock groove. Results:Does the slide lock notch face the rear like its big brothers.
1. The impact of the barrel lug with each shot will eventually push the Slide Lock downward, which can allow the entire slide assembly to propel itself forward off of the frame if the firing pin lug rides over the trigger bar cruciform. (Fortunately, that usually doesn't happen and the slide assembly stays on.)
2. Until that happens, the barrel lug groove finds no Slide Lock groove to engage. That reduces the tightness of action lockup in battery and may increase shot dispersion.
When one understands the function of each part, there will be no future uncertainty of how, why, and when they fit together.