If you come across a record for a full-text item with a green "Check online access" message, this means the library has the item and is able to provide you with access. However, occasionally you will see a message reading, "Your search did not match an online resource at UM. Please log in to request from another library."
Confusing, right? Unfortunately, the OneSearch system has a bug that sometimes mixes up the two different services whose function it is to retrieve lists of online sources for the end user. You can typically correct the non display issue by clicking refresh in your browser until the list of online sources loads. It might take a few refreshes or you could try clicking out of the record and clicking back in.