Part of our job is making sure the forms are properly filled out. Of its not, make sure the sending facility staff/family/whoever knows full well the form is invalid if incomplete and you will have to treat them as a full code.
Sometimes, especially at nursing homes, that's about the most you can do.
I remember one time, years and years ago now, we were sent to a hospital to pick up a patient going to home hospice. Of course when we got there they had an incomplete DNR, and we informed the hospital staff. It was one of those small, "band aide box" type places, the Doc who had set up the transfer had gone off duty already, but the current Doc on duty knew about the case.
Rather than just rubber stamp a new form, he went into the patient's room to have the standard talk about signing a DNR. That turned into like an hour long conversation. Apparently the patient wasn't too thrilled about hospice in the first place and in that conversation, changed their minds and decided they wanted to fight whatever advanced cancer it was they had (I forget exactly).
So we ended up driving back to our base with no patient transport, our company was not too happy, but hey, we ended up serving as a patient advocate by recognizing the incomplete DNR and getting that conversation going.