No they are not. The horizontal and vertical accuracies are as stated above. For now, we decided to put in more digits than necessary for some projections, in order to accomodate the precision needed for others. The instrument measures the elevations to the millimeter level, so we carried those digits through all calculations. 15 centimeters, so use care in interpreting differences smaller than this.
Projections introduce no error, except for the warping that occurs with any projection .
Gridding should not introduce any error, and interpolation introduces error in the sense that it can create data where there was none before. Users uncomfortable with this result may choose not to interpolate. Click on the Error source for an on-line reference. We have plans to implement such a system in the future. We will have some files of this type as we create CD-ROMs and make specialized data products for each region, but we thought it would be more useful to the larger community if we could allow users to select whatever geographic area they desired.