I was intrigued to find Bhutanese yathra-style jackets for sale in Kathmandu. Enquiring of the shopkeeper, I was told that they are woven further out in the Kathmandu valley by ethnic Nepalis, not Bhutanese immigrants.
I guess that the steady stream of Bhutanese pilgrims to sacred sites in Nepal over the centuries would have allowed this cross-fertilisation. Or perhaps Nepalese who had settled in Bhutan and then returned to Nepal may have contributed.
The shopkeeper showed me a genuine Bhutanese jacket on his racks, and the authenticity was evident from the typical and lovely Bumthang colours:
More Bhutanese yathra photos can be enjoyed at Bumthang Yathra