The original data release for K2 Campaign 1 in 2014 used a prior version of the pipeline (v9.2) which only produced "Type-1" FITS Target Pixel Files. The Campaign has now been re-processed using the mature version of the pipeline (v9.3) which updates the pixel files to "Type-2" TPFs (differences detailed here). The new release also adds long-cadence lightcurves, cotrending basis vectors, and collateral products such as smear data.
Finally, the C1 data release notes have been updated to include more details on the data characteristics, and to explain issues associated with the first few days of data which were taken before a pointing tweak.
The reprocessed Campaign 1 data are now available from the K2 data archive at MAST. Campaigns 0 and 2 are currently undergoing a similar reprocessing effort which is expected to be completed in early 2017, at which point all Campaigns will have been processed using the same version of the pipeline.