Hey Mark! We grow a lot of Cucurbita moschata here in Florida and aborted ovaries and fruit occur here as well.
The female flower has an enlarged ovary underneath it, so it may look like a fruit forming but if the flower isn’t pollinated properly, then the ovary will shrivel up and die. But once a female flower is pollinated and fertilized, it should start to enlarge, the flower on the end wilts and dies, and the pumpkin grows and is green (2nd photo). As it matures, it will go from a green to a golden tan color as it approaches maturity. The pumpkin in the 3rd photo is nearly mature and is beautiful! I usually harvest maybe two weeks after this stage.
If the ovaries are turning yellow and falling off, it could be a lack of the presence of pollinators (bees). You can try hand pollinating in the morning by taking a mature male flower and painting the pollen from the anther onto the stigma in the mature female flower (the one with the ovary underneath the flower). Sometimes we have trouble with caterpillars in the flowers, but they are evident from the holes in the petals, oozy sap coming from the ovary, and the frass that they leave behind. Maybe what happened in photo 1?
And still other times, the ovary or fruit will shrivel up and die even if the flower was pollinated. This may be due to a number of factors: the vine perhaps can’t support that many fruit (1-3 fruit per plant is a good target) so some die and fall off, the plant isn’t getting enough phosphorus, or because of something else that I haven’t learned about yet! I also find that the male and female flower ratio is constantly changing and is never balanced. If there aren’t enough male flowers right now, there will be more later.
Anyway, that’s my two cents! Let us know how it goes and what you learn.