You should include a license file in the zip files.
Viewing post in Pixel Side-Scroller Plains Tileset comments
the licence is linked online and the same for all assets and shouldn't change, except probably clarification on certain points.
Since it very well can be that specific questions get clarified in the FAQ (which can happen especially If I release something which is kinda new, e.g. with the controller button packs and/or template sets) and then I'd have to reupload all assetpacks with a new file which simply takes a ton of time whenever this case happens.
If you want to have the licence, just copy paste it and save it from the googledocs.
Thanks for your understanding.