While there is some variance given with Yongey MD's birth year (i.e. his dates are given as either 1628-1708 or 1641-1708), Namchö MD's dates are given quite clearly (1645-1667).
Having read the
Outer Liberation Story of Terton Migyur Dorje and
A Garland of Immortal Wish-Fulfilling Trees, both of which give precious information about Namchö MD, I can say that there weren't any references to Yongey MD in either that I was able to spot.
If the latter dates for YMD are to be believed, then both of them were born within the stretch of 4 years, making them the same generation. However, Namchö was the nephew of Karma Chagmé, and therefore began learning from his lama uncle from quite a young age, and passed into parinirvana quite young as well, living to be only 22. It's quite possible that Yongey MD didn't start studying under Chagmé Rinpoche until Namchö MD has dissolved into the dharmadatu.
Both were students of a great master, and became great masters themselves, so there must be an explanation for why there is no record of contact between the two pupils. Timing and location are my guess... Then again, if Yongey MD was born in 1628, he could've already been a student of Raga Asya when the young Namchö came on the scene.
Does anyone know of any as-yet-untranslated texts which could shed some light on whether the two knew each other and collaborated?
Despite all this, I have heard it said that the incarnations were linked in that Yongey was the continuation of Namchö. Je Tukyi Dorje's
Chariot of the Fortunate, the namthar for Yongey MD, clarifies this connection:
Lord Tsewang Norbu, the great vidyadhara of Katok Monastery who has no equal on this earth, wrote:
"Namchö Mingyur Dorje dissolved into this Lord Mingyur Dorje."
I have heard that Drakpo Nuden Tsal also declared this himself. Namchö Mingyur Dorje began to receive the Namchö in his twelfth or thirteenth year, and thought treasure in his sixteenth or seventeenth. He was due to discover earth treasure in his twenty-third or twenty-fourth year, and was about to open the door to the earth treasures of Dzatö Chijam and other places when he passed away. He therefore demonstrated parinirvana before revealing any earth treasure. It was at that time that Yongey Mingyur Dorje began to open the doors to earth treasure, and it was he who discovered the treasure at Chijam.
Therefore it seems that Namchö transferred his consciousness (perhaps by way of Phowa?
) into Yongey, and thereby allowed him to reveal the earth terma at Chijam which Namchö had been unable to do in his miraculous yet short life.
The closest there is to a mention of Karma Chagmé in CotF is an anecdote about how "When Lama Tarchin of Nemdo Monastery was at the peak of his merit and benefiting of beings his eyes became extremely irritated. [...] He sent two monks to request the treasure revealer's divination." Nemdo (
gnas mdo), or the more phonetically accurate Neydo, is the subsect of the Karma Kagyu that Chagmé Rinpoche founded.