As the TA below attests, keeping clear records of your communications with students in addition to grades and attendance can be essential in resolving questions and conflicts should any arise.
Make sure you are documenting everything, including grades, emails, personal communications, attendance, etc. I had always made a habit of this with my classes, but it really paid off one semester. I was teaching 6 lab sections out of 12 for a large, intro biology course. It was hard to keep students straight with so many sections and there were always several needing to make up labs each week - meaning there were always new faces. I would give the general run down at the beginning of each semester regarding the attendance policy, grading, etc. and had never had an issue with it. About 2/3 of the way through one semester I had a student ask about taking a particular lab exam online and when I would be emailing the password. Clearly, they had not been in lab the week before because we (the other instructor and myself) made it clear that the exam would be taken on laptops provided in class. They never did take the exam. Several weeks later, the class was taking a practical. When I began grading the practicals, I came across one that had 1 answer completed out of 50. I looked at the name at the top and it looked familiar but I couldn't place it. I knew it was not one of my regular students so assumed that they were visiting from another section. I contacted the other instructor as I had several of her students making up the practical with me and sent her their grades. She emailed me back about this same student (the one who got a 1/50) and said that they weren't hers. It took some digging, but I found them on the attendance from the 1st week of class. That was the only time they had attended and it was the same student who emailed me about the password for the previous exam. It was clearly stated in the syllabus that if you missed 3+labs, you automatically failed the class. They were failing anyway with a 0 on one lab exam and a 2% on the other, but the attendance pushed them into the automatically fail category. At the end of the semester, this student emailed me regarding their grade and why they failed. I reminded them of the attendance policy and told them to reference the syllabus. Luckily, the way I took attendance was to have the students sign themselves in each week so they couldn't argue. The student’s parents ended up getting involved with the dean, claiming that there were medical issues. Again, I had kept a doctor's note this student gave me (the first and only week they had come to class). I thought it was odd at the time but put it in my folder anyway - the note stated "medically cleared to return to class". This was the doctor's note the parents were referencing when they said there were medical issues which did not allow their child to attend class. All of my documentation ended up going to the dean of the department and he handled the issue with the parents. I'm SO glad I kept every email, paper, attendance form, and exam that this student did or did not do.