I have been working on a CIF data file based on experimental data [1] (free full text isn't available, but the page 2 with the experiment details can be found in the free preview provided by Springer).
Unfortunately, I don't know an awful lot about crystallography parameters (although I have been consulting the CIF core dictionary). The CIF file I linked to was created using EnCIFer & VESTA (I mostly used VESTA to get a handle for the text formatting of CIF files). The non-coordinate data mentioned in this paper includes:
\begin{array}{ll} \hline Z & 4 \\ \text{Formula} & \ce{C9H7N7O2S} \\ M_r & 277.3 \\ \text{Coordinate system} & \text{monoclinic} \\ \beta & 105.99^\circ \\ a & \pu{4.488(2) Å} \\ b & \pu{31.886(4) Å} \\ c & \pu{8.067(2) Å} \\ V & \pu{1149.5 Å^3} \\ D_m & \pu{1.59 mg mm^{-3}}\\ D_c & \pu{1.60 mg mm^{-3}} \\ \lambda & \pu{0.7107 Å} \\ \text{Space group} & P2_1/c \\ \text{Crystal dimensions} & 0.7\times 0.1 \times 0.7\, \pu{mm} \\ \hline \end{array}
The problem is that Accelrys DS Visualizer so far renders my CIF file as:
Notice how some of the hydrogen atoms are disconnected from the main chunk of the azathioprine molecule.
- Acharya, K. R. Proc. Indian Acad. Sci. (Chem. Sci.) 1984, 93 (2), 183–187 DOI: 10.1007/BF02842141.
Answer
The coordinates of the hydrogen atoms of the methyl group in question are there (H16a, H16b, H16c).
The problem is a rendering problem of the Accelrys visualizer.
Other tools don't have a problem with this CIF file. The image below is a medium-quality PovRay rendering generated through PLATON. 
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