Here is more info on 852.
http://journals.fcla.edu/fshs/article/viewFile/86346/83262Some main points, US-852:
*is resistant to Phytophthora nicotianae, citrus tristeza virus, and citrus nematode.
*is a hybrid selected from several dozen siblings produced by a cross of Changsha mandarin (Citrus reticulata Blanco) with English Large Flowered Trifoliate Orange (Poncirus trifoliata[L.] Raf.)
*only about half of seedlings recovered are of nucellar (apomictic) origin so that they have uniform morphology typical of US-852.
*cuttings of US-852 root easily, but a sizable proportion of these never develop well-anchored plants that produce vigorous growth of scion buds.
Also a patent application has been filled for this cultivar in 1998, I guess expired after 20 years.