Answer: There has been recent work in camellia breeding to increase winter hardiness. The Ice Angel series for instance includes some rated hardy to zone 6 as described in the Monrovia online plant descriptions. The microclimate at the planting site, the weather each year (eg periods of drought followed by sudden temperature drops, oscillating temperatures in spring, snow cover, etc.) and the overall health of the plant can also have a strong influence on hardiness in individual situations, and to some extent hardiness ratings can be subjective as a result, too, as some are more conservative than others when describing hardiness. For example, the National Arboretum -- where it was developed and introduced -- indicates a hardiness rating of zone 6B for "Snow Flurry" whereas Camellia Forest Nursery catalog indicates it is hardy to -10; personally, I would consider both to be reliable sources.
In my experience it is usually a good idea to inquire locally and see which camellias gardeners are having consistently good results with. That way you can have a local reference in terms of the particular plant's response and performance with your local weather patterns. I hope this helps.
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