Ino this day and age we know that documentation is key. No matter how brief the communication or even if there wasn't any, it's always better to be safe than sorry. Email can not be trusted. Too easily hacked and deleted. The only records one can trust are ones they keep. And since this would be part of your teacher notebook and considered your property, you control access to it so u know it can't be modified. Sounds paranoid yes but I have seen things like this happen to several teachers. Document document document and where possible use your own materials.