Bhaji, ONE question. Have you done your own research? It seems you are just copying the birth years from other (not-trustable) sources.
The Bani in SGGS is not of Sheikh Farid that lived during the 12th century. But a Bhagat Farid that lived latter. One of the most learned persons in the panth, was Bhai Kahn Singh Nabha, and he himself has stated this.
I am writing on this currently... As I'm not in India, I can't do certain things. But you being in India, should atleast visit the Gurdwara in Ayodhya where the Bhagats supposedly met Guru Ji (Bhagat Ramanand, Bhagat Ravidas and few others).
Bhul Chuk Maaf,
WJKK WJKF
I have not copied the data /dates from any site. I have read them in the book - Bhagat Saints of Shri Guru Granth Sahib Ji written by Shamsher Singh Puri published in 1999.
He is a very learned man and has also authored -
1. Prayer
2. Handbook of Sikh Theology
3. Happy Marriages - The Sikh Way
4. Ills of Today's Fast Life - The Sikh Therapies
5. Influence of Thought on Body and Mind - The Sikh Perspective
6. Varan Bhai Gurdas
So I can't say him to be a 'non-trustable'.