Hello Adrian,
At first glance there seems to be little rhyme or reason to having it or not. A shovel, if installed, is usually on the platform just forward of the Glacis plate. I usually see the snow shovel installed face up, but at times it appears stored face down. Since few Tigers were photographed in detail from all angles, it is possible that a shovel was attached elsewhere so that we do not see them in the images at hand.
Early in the war some companies in Tunisia show a spade or no shovel in sight, while some do not. Many Tigers early in the war to the eastern front had an almost flush fitting flat shovel or the snow shovel, but later in the war most of these no longer have them - even in winter photos.
Shovels are rarely seen on western front combat veteran Tigers, and by July/August most of these have disappeared from view. Most images of Liebstandarte 3rd Co Tigers taken in 1944 before D-Day show the shovel, and with spade down. A popular series of photos in May 1944 shows Tiger I of Lieb. No 311 with Westerhagen with its shovel in place, and with the spade pointed up. Yet photos taken after D-Day show it (and most other Lieb. Tigers) without the shovel. Maybe these interfered with some operation?
A modeler who wants to be accurate needs to find and study images of the Tiger (or at least the Tiger's company), ideally taken the period which his Tiger represents.
Hope this helps solve any confusion by adding to it
