These images are raw replicator data. There are artifacts on the substrate, consisting of frost growth resulting from evaporative cooling of the formvar solvent. The artifacts are generally much smaller and have higher concentrations than the crystals. Scratches on the substrate are not uncommon, and to a lesser extent dust contamination may also be present.
Particle identification for quantitative analysis of replicator data, using image processing software, is accurate because each particle is confirmed by a human. Viewing the data through the microscope shows data quality that is much better than these images, and the issue of data vs artifact is rarely ambiguous.
Crystals in the lower parts of the altitude profile are generally rounded and have indescript shapes because this is the sublimation region of the cloud, where crystals are falling into ice-subsaturated air. Crystals in the mid-cloud often have pristine crystal shapes (columns, rosettes, plates, etc.). Often there is a layer of small and quasi-spherical crystals near the cloud top, where crystals nucleate.