Here's some history:
The first car to carry the name of Professor Ferdinand Porsche (1875-1951) was the Type 356. All the cars produced by Porsche prior to the 356 designation bore the name of the companies that had engaged the Porsche engineering firm (Mercedes, Wanderer, Auto Union & of course Volkswagen). The first Porsche is now referred to as Number 1. But in fact, Number 1 actually carries the number 356-001.
Some may first think that the 356 was Professor Porsche 356th design, but in fact it was only his 349th. Back in 1931, Porsche was comissioned by Wanderer to design a 2.1-litre vehicle. Not wanting to to give the impression that this was to be his first design in the automotive field, Professor Porsche designated the Wanderer project as #7. This might have been an unnecessary ruse, but Porsche was a cautious man who was aware that some of his potential customers might be suspicious of his inexperience.*
*excerpt taken from Original Porsche 356 by Laurence Meredith.