The collection records show this plant to have been added in 1999, sourced from Burncoose Nursery. I need to ask them if they recognize it, though it doesn’t seem to be anything in their current catalogue.
The register description for the variety is:
Carter’s Sunburst. (C.japonica), American Camellia Yearbook, 1959, p.269, Reg. No.367: This seedling hybrid (japonica x reticulata) was originated by E.H. Carter, California, USA. First flowered 1951. The leaves are large and medium green. The flower averages 13.5 cm across and is pale pink, striped deeper pink. They vary in form from semi-double, through peony form to formal double on the same plant. Flowers mid-season to late. This cultivar is now considered to be a straight C.japonica with no C.reticulata in its breeding. It has produced a family of sports including: Carter’s Sunburst Blush, Carter’s Sunburst Pink, Carter’s Sunburst Pink Variegated, Carter’s Sunburst Variegated, Chow’s Han-Ling, Han-ling Raspberry, Han-ling Snow, Carter’s Sunburst Sweetheart. Synonym: ‘Carter’s Sunburst Regular’. Orthographic error: ‘Carter Sunburst’. Chinese synonym: ‘Dakate’. For colour photos see p.74, Macoboy, 1981, The Colour Dictionary of Camellias and on p.21, New Zealand Camellia Bulletin, vol.V, No.2, 1967. This Camellia has received the ACS. “National Camellia Hall of Fame Award” for 1978, the SCCS. “Margarete Hertrich Award” for 1963, and ‘John Illges Award” for 1964 and the RHS, “Award of Merit” 1977.
There is another plant under the same name in the collection at 1H-003 which I believe to be correct. This plant has single to just semi-double blooms, sometimes bicoloured, sometimes not, varying in their shade of pink.