The Goindwal pothis are volumes of hymns compiled in the time of Guru Amar Das Ji, before the Adi Granth of 1604, and they are the earliest Sikh manuscripts in existence.
Two are generally reported to survive, held by descendants of Guru Amar Das Ji's family, at Ahiyapur near Jalandhar and at Pinjore.
They matter because they show what the collection looked like before Guru Arjan Dev Ji's compilation: which hymns were in it, in what order, and with what variations. That is the direct evidence for how the scripture was assembled.
Access is restricted. A small number of scholars have seen them and published descriptions; most have not.
The pattern is the same as the Kartarpur birh: the documents that would settle the questions are in private hands and the questions therefore stay open.
This is not a criticism of the families, who have preserved them for four hundred and fifty years, which is why they exist at all.
The pothis are volumes of hymns compiled before the Adi Granth, held by descendants of Baba Mohan, and they are the closest thing to a source document for the compilation of 1604.
Two are known and are in family custody. Access has been very restricted and the scholarly examinations of them are few.
What they would settle, if they were properly examined and published, is how the volume was assembled and from what. That is the central question of Sikh textual history.