How to add new reference in entity reference field in node edit form keeping old references intact and hidden? In my project, there is a content type 'song' containing an entity reference field to reference content type 'playlist'. More than one user can edit a 'song' to add it to their own 'playlist's.

Now, when one user updates a 'song' node creating his/her references in the node edit form, the previous references made by another user are deleted. In the node edit form, the field is formatted through an entity reference view showing a list of 'playlist's only created by the current user. The number of values for the entity reference field is set to unlimited.

What would be a good and server-friendly approach to solve this problem keeping in mind that there can be an unlimited number of previous references made by other users?
Edit the field and set number of values to be unlimited. If you want more control and flexibility you could put the entity reference within a field collection.