Patent attorney Stephen Nipper recently posted on his blog, The Invent Blog, a question about re-examination numbers. It seems that the USPTO website has some erroneous examples of re-examination document numbers.
In brief, anyone may file a request for a rexamination of a patent on the basis of prior art consisting of patents or other publications. The USPTO will examine the prior art and decided whether some, all or none of the claims of the patent in question should stand. At the end of the review the USPTO issues a re-examination certificate that sets forth the results of re-examination. This certificate is then attached to the original patent.
Re-examination certificates are not indexed in the USPTO's web-based patent database. Instead, users can retrieve a copy of the certificate by retrieving the original patent, e.g. by searching the patent number and clicking on the "Images" button to see the TIFF image. The re-exam certificate is attached after the claims section. (See 3,876,375.)
When a request for re-examination is filed, the USPTO assigns the case a control number preceded by a series code. The series code 90 is used for ex parte re-examination proceedings (90/009,335) and 95 for inter partes proceedings (95/001,115). Since 1981 there have been approximately 9,500 ex parte re-examinations filed. And 500 inter partes re-exams have been requested since November, 1999. The number of requests has nearly doubled in the last decade, increasing from 350 in fiscal year 1998 to 650 in 2008.
It is possible to retrieve re-examination filings in the USPTO's Public PAIR (Patent Application Information Retrieval) System. Simply search the re-examination control number (including the series code, e.g. 90/010334). The file wrapper will contain all the documents and forms involved in the re-examination, including a copy of the patent in question, submitted prior art, e.g. patents and non-patent literature.