The "Window" object type in TestComplete is described in https://support.smartbear.com/testcomplete/docs/reference/test-objects/controls/desktop/general/window/index.html
Basically, the three fields are, in order from left to right, the WndClass, the WndCaption, and the Index... the number "1" is not position, but an "index" of objects... if there are, for some reason, two objects with the same WndClass and WndCaption, then there would be one with a number 1 and one with a number 2.
The reason why it works fine without the 1 in your example is because there is no other object with that class and caption... so, the index is superfluous.
