All About Miniature Roses (1967) 
Ralph S. Moore
Chapter 18 — Searching for Better Varieties

More recently several lots of self-set seeds obtained from a plant of the China rose Old Blush (Parson's Pink China) supposedly in cultivation before 1759, were planted and the seedings observed. In all three lots, gathered in different years, the germination was only fair to poor. But Old Blush produces hips readily and each hip contains several medium size seeds. From the first lot quite a number of the seedlings were very definitely of the miniature type. One plant which has grown no taller than 10 inches in seven years has tiny leaves and tiny miniature pink buds opening to one-inch pink flowers (same color as R. rouletti) with seven or eight petals. It has on occasion set a few seed hips.

From the same lot also came other miniature roses ranging in height from 10 to 12 inches. Most of these were very bushy with double one- to one and one-fourth-inch flowers ranging in color from pale pink to medium rose-pink. One of these produces orange colored hips containing one to three seeds none of which appears to contain an embryo. Another grew into a dense free blooming plant with flowers almost duplicating Pink Joy (which is a self seedling of Oakington Ruby). Cuttings of this plant were difficult to root. Still another one of these seedlings grew not over 8 inches high and bore soft pink double flowers resembling Peggy Grant. Cuttings of this were also difficult to root.

The only seedling of the lot to be introduced was one which has slightly larger foliage and lavender-blue (or magenta) colored semi-double flowers. This selection, Mr. Bluebird, grows readily from cuttings and has proven quite cold hardy. Some seed hips are produced, carrying up to five seeds, but germination is very poor. However, among its self seedlings have been several growing not more than 6- to 8-inches tall with miniature leaves and tiny double flowers usually not more than one-half to one-inch in size. Petals are usually very narrow (lance shaped). No seeds have been observed on any of these seedlings but some pollen is produced.

Notes:
Moore wrote that his first Old Blush seedlings were raised in 1957. Mr. Bluebird came along "More recently". The point is that his memory would not yet have been greatly dimmed by the passage of time as he wrote this book.

And the following item is worth considering when people doubt that Old Blush could produce minis:

J Royal Hort. Soc. 66: 73-82, 242-250, 282-289 (1941)
Notes on the Origin and Evolution of our Garden Roses
C. C. Hurst, Sc.D., PH.D., F.L.S.

Parsons' Pink China is a diploid with 14 chromosomes in the body-cells and 7 in both the male and female germ-cells. Although a diploid, its chromosomes are not regular in their behaviour and weak pairings in the germ-cell divisions lead to defective pollen and embryo-sacs and consequent sterility. In this respect the Pink Chinas behave as hybrids rather than pure species.

Burbank (1914) offered a similar example with his Paradox walnut (a hybrid of Juglans regia and J. Hindsii). In the second generation, "there will be bush-like walnuts from six to eighteen inches in height side by side with trees that have shot up to eighteen or twenty feet; all of the same age and grown from seeds gathered from a single tree. This rate of growth continues throughout life, and the fraternity of dwarfs and giants has been a puzzle to layman and botanist alike."