For the 2MASS Sampler only, all apparitions of objects detected in the scan-to-scan overlap regions have been included in the Release Catalogs. This has been done so that users can use the redundant observations to assess photometric and positional quality, keeping in mind the known caveats on photometric (cf. III.4.e) and astrometric (cf. III.4.d) biases. All future 2MASS Catalog releases will rectify multiple detections in the scan overlap regions, and will included only one apparition of multiply-detected objects.
Up to 10% of the sources in the 2MASS Sampler Point and Extended Source Catalogs may be redundant, because they fall in the overlap regions.