I have various signup forms on my website, all adding to 1 list in MailChimp. Each signup form has different purpose, e.g. free ebook, video etc. By using a hidden source field I managed to provide the correct download urls etc.
But... How to handle a visitor who signs up on multiple forms? I want to share the related materials with him, but MC marks the duplicate as error and requests to update profile... with no option to obtain the related material.
You'll probably need to use the API to make this work, a simple form isn't going to cut it.
There are some options. If there are only a handful of things, have them be interest groups. When someone signs up, say for a free ebook, mark the free ebook interest group and subscribe them if necessary.
You can then create an automation for each interest group to send the material.