Satguru is a form of Akal Purakh and is absolutely perfect. Gurbani says clearly, ਭੁਲਣ ਅੰਦਰਿ ਸਭੁ ਕੋ ਅਭੁਲੁ ਗੁਰੂ ਕਰਤਾਰੁ ॥ - “Everyone makes mistakes; only the Guru and the Creator are infallible”
Further, Satguru is the incarnation of Shabad. Gurbani and Guru are one and the same. ਬਾਣੀ ਗੁਰੂ ਗੁਰੂ ਹੈ ਬਾਣੀ ਵਿਚਿ ਬਾਣੀ ਅੰਮ੍ਰਿਤੁ ਸਾਰੇ ॥
So it would be inconceivable that Satguru could recite Gurbani incorrectly.
“Satguru” Jagjit Singh however often made errors in reciting Gurbani. They are errors anyone could make and are expected of a Sikh. But they are impossible for a Satguru.
For example, in the video below at 6.06 the verse is recited “tan man seetal hoi” when the correct tuk is “ man tan seetal hoi”.
Again at 9.50 in the video below the tuks is read “Jo gur kahai so bhal kar mano, har har katha nirali” when the correct tuk is “Jo Gur kahai soi bhal mano”
At 17.05 he incorrectly says “jio kookar joothan moh pai” when the correct tuk is “jio kookar joothan meh pai”
At 18.09 he reads the tuk “ਮਨੁ ਸੁ ਮਧੁਕਰੁ ਕਰਉ ਚਰਨ ਹਿਰਦੇ ਧਰਉ ਰਸਨ ਅੰਮ੍ਰਿਤ ਰਾਮ ਨਾਮ ਭਾਖਉ ॥੧॥. But he reads the word hirday as hirdai (with dulanvan).
In the video below at 1.10, he recites, asa sabhai lahi kai iko aas kamao when the correct tuk is “ika”
It is inconceivable that Satguru who is the embodied form of Shabad could incorrectly recite Gurbani.
This is just from the very few videos we have seen of his talks. I am sure there are many other mistakes in the videos that I have not seen.
How can anyone claim that the Namdhari leader was in fact the Satguru in the same line as Satguru Nanak?