There are layer numbers and layer numbers. ADE provides a layer number for each type of object. Some objects such as aprons, taxiways and runways use a surface type and ADE tries to display these in the same way so that the different surface types will cover each other in the same way as in the simulator. In other cases the layer number for the object exists only in the ADE display to allow the user to reorganize the order in which objects are displayed. Users can change some of these to make it easier to work with the airport when one object covers another that you want to get to. In some cases you cannot change the display order (layer number) since this mimics what you see in sim. ADE also limits the layer that some object can be in. Again this is done to assist the user in working with overlapping objects. There are upper and lower limits for some objects so that they can't mess up each other. Terrain for example is in layers below airport elements and can't usually be moved above them. GP Objects have their own rules as far as layer is concerned and this reflects how they cover airport objects and also how to change them: https://scruffyduck.screenstepslive...the-layer-number-for-custom-gp-objects-in-ade
As to your other post. ADE will probably not offer you the chance to change layers on something that is fixed in the Z order like an apron surface. In settings there is an option to Ignore Layer Constraints. Select an Apron and the move forward and back are not visible unless you have this checked. However if you select a generic building then you can move it forward or backward in the display.
If that is checked then you can move things up and down at will but you will lose the extra function of ADE in trying to tell you what overlays what in the sim. Folks complain sometimes that such and such an apron is missing when it is actually hidden under another.
Finally the right click menu gives access to an option to Reset Default Drawing Layers. If things get really messed up then you can use this to get stuff back to the start in the Z -Order