In ODF 1.1 the description for chart:class=chart:surface is:
the data points are interpreted as tabular data, where each value defines a 'height' at a specific grid location.
In the ODF draft 1.2 this has changed to:
The values of multiple <chart:series> (marked as being of type chart:surface) are interpreted as a 'altitude' at a specific grid location.
So in 1.1 one needs only one series to give the tabular data (table range) for a whole surface where the column/row location indicates the grid location for this "height".
In 1.2 on the other hands an undetermined number of series are supposed to be combined in an undetermined way to create the surface. (Some appear to interpret this to mean that each series gives the heights for one fixed coordinate and the series contains rather than tabular data a sequence of heights for the various values of the other coordinates.)
As a consequence the 1.1 description allows several surface plot to be placed in the same chart. SInce there is no way to determine which series would belong to which surface, in 1.2 this has been removed.