Hi there!
You are free to use any other drawings or graphic material you can get, that’s not a problem. What we mean when we say that the material we provide is the only one valid within the context of this competition is that if there are any discrepancies between the material we provided and the one you found elsewhere, then the one we provided prevails.
Imagine for example that a new street has recently been created, and one drawing shows it and the other one doesn’t. In a case like that whatever the drawing we provided shows is what should be considered as real within the context of the competition.
Hope this answers your question 🙂