There is no official "formula sheet" for the Astronomy C event. I believe you are referring to the sheet on the Scioly.org website (http://scioly.org/wiki/images/c/c6/Formula_Sheet.pdf), which was made by competitors, not event supervisors. However, there are helpful formulae and examples on the Coaches Manual CD.
When grading numerical answers, supervisors always should accept a range of answers, usually plus or minus 10% of the value on the key. This guideline is shown on the sample tests at http://soinc.org/sites/default/files/uploaded_files/Astronomy_ES_GUIDE_C15.pdf and http://soinc.org/sites/default/files/uploaded_files/AnnotatedRegionalAstronomyTest15.pdf. A nominal range can be explicitly due to competitors having slightly different physical constants or tabulated values depending on their resource.
Yes, students could be asked to identify incomplete specimens. Samples requiring identification should show specific features making identification reasonable. A bone fragment would usually not be enough to make a solid identification, but a tooth or claw might be.