Our IEP team is careful to say to our student's parents that it is our recommendation that their student is in the correct placement for the upcoming year. Our unit classes include students that have severe intellectual disabilities. When we have our general ed teachers talk about what standards the general ed students are currently working on, the parent's are sometimes shocked.
At our school, we haven't had any issues with failing to assemble an appropriate IEP team. Our administrators do a great job of ensuring that all IEP team members know what is expected of them. We have sped meetings weekly to ensure that we stay on top of IEP due dates and re-evaluations.
I believe that there is less oversight on the substantive side of IEP implementation accountability. In two years I've never had my progress monitoring checked by anybody. I've also never had parents inquire as to how their child is progressing towards their IEP goals.
Regarding implementation errors, I don't think I've ever seen an administrator verify the services provided by different related service providers such as speech or OT/PT. It may be assumed that these related services are professionals and that they will do their duty to maintain fidelity to the IEP.