Did all the Bhagats receive the GurMantar from Guru Sahib?

There is no concept of any GurMantar according to Gubani written in Guru Granth Sahib.
Guru Nanak Sahib did not collect the Bani of any Bhagat. Please go through the following article for knowing the facts and details:
http://www.geocities.ws/sarbjitsingh/Bani6010EngMag20161111Version.pdf
The Bani of Bhagats started getting collected from the 3rd Guru Sahib onwards.
Most of the Bhagats have adopted the format of Guru Granth Sahib.

When we try to analyze on the basis of Guru Granth Sahib, we find that Guru Arjan Sahib has referred to 10 Bhagats, Guru RamDas Sahib has referred to 7 Bhagats and Guru AmarDas Sahib has referred to only 3 Bhagats. Whereas Guru Nanak Sahib and Guru Angad Sahib has not referred to even a single Bhagat. This observation proves that information about these Bhagats might have started getting received during the period of AmarDas Sahib and with the passage of time there was increase in the information. This might be the reason that Guru RamDas Sahib has referred to 7 Bhagats and Guru Arjan Sahib has referred to 10 Bhagats.
Both the Guru Sahibs and Bhagats have mentioned that they have learned and achieved this high status because of the complete Guru (“ਪੂਰੇ ਗੁਰ ਤੇ ਗਤਿ ਪਾਈ”). In Guru Granth Sahib it is clearly mentioned that complete Guru is the Shabad Guru. Many a times it is mentioned about the physical Guru’s of these Bhagats in the prevailing history. But they might not have achieved the completeness; otherwise there should have been some mention about them in Guru Granth Sahib. Even these Bhagats have not mentioned about their physical Guru’s in any of their Bani present in Guru Granth Sahib. This clearly shows that these Bhagats would have adopted their Guru as Shabad Guru as taught by Guru Nanak Sahib.
The Gurbani written in Guru Granth Sahib proves that all the 15 Bhagats might have been after the period Guru Nanak Sahib and all these Bhagats might have got guidance to write from the Bani of Guru Nanak Sahib.
The compilation of Gurbani was done by the 5th Guru Arjan Sahib. During that period, itself people started spreading the adulterated Bani in the name of Nanak. Till today many of them are common. Most of the invitation cards of the marriage card being printed have adulterated Bani and not Gurbani. Similarly, the adulterated Bani of Bhagats also started getting spread when they were given proper respect by entering their Gurbani in Guru Granth Sahib. Those Shabads of the Bhagats which have not been included in Guru Granth Sahib, either do not belong to the Bhagats or they were not available till the compilation of Guru Granth Sahib.