Welsh is stated in several sources as having been crossed into Chincoteagues. A Chincoteague Pony management plan from 2014 stated that "A wide variety of breeds such as Morgan, Welsh, Shetland, Arabian, and Mustangs were placed in the Chincoteague pony herd to increase genetic diversity and vigor among the present stock". The Wonder of Ponies, published in 1980, writes that, "an infusion of Welsh blood led to the ponies’ becoming smaller and, in addition, gave them dapple-gray coats."

Clarence and Ralph Beebe appear to have been partial to Welsh outcrossing. The early 1950s Beebe Ranch bred grey mares Beaufort Blue Bell and Beaufort Misty appear to be part Welsh. In 1959 an advertisement for Beebe Ranch stated that half Chincoteague and half registered Welsh ponies were for sale. A Welsh stallion appears to have been living at Beebe Ranch in the early 60's as Hoofprints in Time says that a "fine Welsh stud" survived the 1962 nor'easter.

Beaufort Blue Bell, from Ponies for Young People by Ehrman Mitchell.

Beaufort Misty and half Welsh colt Once Again, from Beaufort Farms scrapbook

A silver bay Welsh Pony stallion named Starlight was owned by Beebe Ranch and sired half Chincoteague foals. Ralph Beebe was intending to breed down the size of his Chincoteagues using Starlight. A visitor to Beebe Ranch wrote Marguerite Henry and indicated that Starlight had sired Chincoteague foals in 1957 and 1958. He was bred to Misty in 1958 and 1959, but it appears she did not take and her 1960 foal was sired by a different stallion.

Starlight and Misty, from the Pictorial Life Story of Misty

Bayside Farm located in Berlin, Maryland,  near Chincoteague, bred half Welsh half Chincoteague Ponies in the 1950's and 1960's. One of the farm's ponies, Bayside Prince Charming, was in the 1961 movie Misty playing the Chincoteague Pony Watch Eyes. It's likely that some of the half Welsh ponies became part of the Chincoteague bloodline. Ponies for Young People described Bayside as breeding Welsh into the Chincoteague Pony. The farm brought ponies to be sold at Pony Penning at some point in the 1950s. Their chestnut roan stallions Farnley Morning Star and Farnley Sun Star may be the source of sabino roan in Chincoteagues. It's long been rumored a Farnley bred Welsh stallion was the source of this color, but this cannot be confirmed at this time.

Farnley Morning Star, from The Chronicle of the Horse

Farnely Sun Star, from The Waynesville Mountaineer

Bayside Farm Chincoteague Pony Mares and their half Welsh foals, from a 1959 Daily Times advertisement.

Half Welsh Bayside Prince Charming who played Watch Eyes in Misty (1961)

The Burton family of Chincoteague raised ponies for many years, including Chincoteagues, on their farm which is now Tom's Cove Campground. A silver black Welsh Pony stallion named Silver King was owned by the Burton's in the early 1960s. Marguerite Henry and Wesley Dennis rode in a cart pulled by Silver King at the premier of Misty on Chincoteague. He's pictured twice in A Pictorial Life Story of Misty. With outcrossing being commonplace in that time period and Beebe Ranch breeding half Welshes at the time it's possible that Silver King became part of the Chincoteague bloodline. There's also some hints that he may have been the sire of one of the movie Misty's, named Emma.

Silver King, A Pictorial Life Story of Misty

Silver King, A Pictorial Life Story of Misty