Asked the same question in 2010 but no one came forward with an answer.
It would seem that in 1870 there were two census enumerations taken in Philadelphia. The index to the first enumeration is Philadelphia, PA 1870 Census Index. 929.3748 P53p. Look at the addenda in the front of this index for Wards 27 and 28. There is no index to the second enumeration. There are, however, descriptions on microfilm of many of the second enumeration boundaries. These boundaries are also shown graphically in a series of drawings at the Map Department.
Apparently the 1870 census was filmed twice. The second filming (2nd) is listed first and is usually easier to read. However, since some of the records were faded
or lost between the first and second filmings, it is best to search the first filming
(1st) whenever the material on the second filming (2nd) is too light to
read
http://freepages.genealogy.rootsweb.ancestry.com/~stephan/research.aids/1870.htmlThe instances where there was a second enumeration usually were the result of local officials challenging the accuracy of the results of the first count. These challenges were fairly common in localities which were rapidly growing or changing. Most such challenges were turned down by the census officials and/or the courts but some did result in additional enumerations.
There are apparently 2 versions of the 1870 NYC Federal Census that are listed as 1 st and second enumerations. In 1870, enumerators failed to record addresses in New York City. Addresses serve the same purpose for census officials as citations for genealogists. Without documentation, census officials could not refute allegations that households had been missed. Census superintendent Francis A. Walker ordered a recount. (Recounts were also made in Philadelphia and Indianapolis.3) These recounts are known as the 1870 Second Enumeration. The first enumeration occurred in June 1870 and the second about six months later.
http://ancestryinsider.blogspot.co.uk/2011/09/darned-second-enumerations.html Sandra
