They can't all be gems...that being said, let me play devils advocate, just a little!
What grade is your son in? If he is K,1, or 2, then you probably need to be so invloved, but if not, then you don't, unless your son has an IEP or 504 plan that calls for you to check his home matierials, or needs one for organization and it just has not happened yet, then you should not be needing to verify the details so much. Writing down the homework assignment and completing homework independently is an age appropriate skill that he should be able to accomplish by himeself. Frankly, I would stay out of it, and if your son misses something, then the issue is going to be clear to everyone.
Our job as parents is to provide a quite place and time for our kids to do homework and to help them when they have questions. The child should be doing the homework, and should be learning how to gather the information and materials they need to do what is expected of them. If he does not know how to gather that information from the teacher the way she teaches, then his work should reflect that so that the teacher can sort it out. That is her job. He won't be perfect every single day at bring home this information, but even when he fails, he learns how to improve. They expect that some learning experiences will result in less than perfect output, but more than withwhile lessons about personal responsiblity and organization. If your son has an issue with independent work and organization, then you need to know how severe it is, and so does his teacher. You do him no favors by playing middle man on getting the homework assingments straight for him.
The teacher does not sound to be concerned about it. Your son must not be too concerned, because children who are experiencing grief from a teacher due to not completing homework do ususally no love that teacher. You are upset about it. You are not going through school for a year, your son is. You should not be hunting on the website for his assignments, he should. Let him handle it, and provide him a quiet spot and time to do his homework with your support and affection, and not much else. If he comes home no knowing what to do, do not bail him out. If he goes to school without anything, and something was assinged, he will know where the problem is, and he should be the one to learn what the concequences are, it won't mean anything to him unless you let him handle it himself.
If you are thinking that he can't do that, then that is a much different story. Only by backing off will you get down to the nitty gritty of the ancilary skills your son needs to learn independently, and he may need some help or assistance to do that, but probably not from you. From the "been there, done that" category here, let him have a few bad days and find out how deep it goes. Then hold the school accountable for teaching your son every thing he needs to learn to be successful. You are not at the school with him, so you really have no idea what is happening, and you might be very, very surprized at how things are at school. Our children are often very different at school than we realize.
If it is just this teacher, then she will never know if you keep meddeling in it either. Who knows, you may have a whole brigaged of parents who feel like you do, who are not bailing out their kids and finding things for them to do, and she is holding up your son as an example of the children who get how she teaches...
One thing is for sure, uless this is high school, there is not a permanant record, and a few bad days is not going to cascade into the begining of the end. He has a much bigger lesson to learn here than anything that is on a single work sheet!
M.