Basic data on depressive symptomatology, United States, 1974-75 / [Rona Beth Sayetta and David P. Johnson]. (OCLC #5833792)

To search for a Sudoc number in OCLC (like “HE 20.6209:11/216”), use the gn: index, and remove all punctuation and spacing from the number:

gn: HE20620911216

This search does return the title we’re looking for:

Vital and health statistics. Series 11, no. 216
HE 20.6209:11/216

but also this one, whose Sudoc number compresses to the same string:

NCHS CD-ROM. Series 21, no. 6.
HE 20.6209/11:21/6

This is still a useful search, to quickly get you to government document records (if they exist), but since that compression to the search string is lossy, you must confirm that any record you find this way is the correct one.