NARA released the 1950 population census schedules for researcher use on April 1, 2022, at https://1950census.archives.gov.  This is the 61st in a series of blog posts on the 1950 census. 

Good mistakes sometimes happen.

In 1952, the Census Bureau microfilmed only the population side of the 1950 Census.  The reverse side was not microfilmed.  When someone arranged the census schedules for Enumeration District 72-5, Luquillo Municipality, Puerto Rico, in their portfolio, one sheet was placed "housing side up."  A mistake!  The microfilm camera operator filmed the housing side - then - realizing the problem - flipped the page over and filmed the population side.  Thus, researchers interested in persons residing in dwellings with the serial numbers 55-60 in that ED will have both the information about the people and their dwellings.  (Serial numbers were numbers assigned sequentially by the enumerator in column 3 as a way to easily count the dwellings in the ED.)

Detail from Reverse (Housing) Side of Forma P93, Censo de Población y Viviendas:  1950:  Puerto Rico, Sheet 8, ED 72-5, Luquillo Municipality, Puerto Rico, 1950, showing information about the six dwellings that housed the people on the other side of the schedule. 
Detail from Reverse (Housing) Side of Form P93, Censo de Población y Viviendas:  1950:  Puerto Rico, Sheet 8, ED 72-5, Luquillo Municipality, Puerto Rico, 1950, showing information about the six dwellings that housed the people on the other side of the schedule.

And here is the "front" or population side of the same sheet:

Front (Population) Side of Forma P93, Censo de Población y Viviendas:  1950:  Puerto Rico, Sheet 8, ED 72-5, Luquillo Municipality, Puerto Rico, 1950, showing information about the people for whom dwelling information is available (Dwellings serials 55-60). 
 Front (Population) Side of Form P93, Censo de Población y Viviendas:  1950:  Puerto Rico, Sheet 8, ED 72-5, Luquillo Municipality, Puerto Rico, 1950, showing information about the people for whom dwelling information is available (Dwellings serials 55-60).

Thanks to Jackie Budell for her research assistance!