I am certainly not an expert, but I do know for a fact that different armoured divisions within the Wehrmacht had a numbering system based on which vehicle it was within a particular platoon, within a particular company. You will also find that some tanks would use Roman numerals or the letter R to designate command tanks. A great resource are the three books written by Bruce Culiver entitled Panzer Colors. I saw these books in my latest Squadron catalog and should be on their website. They go through all the different painting schemes as well as the numbering system and tactical and divisional symbols used.