I've just gone back into my EA files and found the image and media libraries are populated with the images and clips from all the buttons. Possibly, I'll need to save each button and associated files in a separate folder.
I'm new to EA, and finding it's not as intuitive as other Adobe software. The 'idea of less is more' gets taken a bit far sometimes. Hidden keystrokes, with modifiers – Mac has no right click option, instead we use ctrl click. To update an asset in Muse, ctrl clicking the item in the asset panel displays the option to update. This may well be documented, but I only found this by accident. InDesign has got it right, why can't other Adobe Apps use the same methods, for navigating, updating and deleting.