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ਗੁਰ ਸੇਵਾ ਜੁਗ ਚਾਰੇ ਹੋਈ ॥

According to gurbani, Satgur bajhu gur nahin koi ie Guru Nanak Sahib is the only true Guru.
Does the above pankiti mean that Guru Sahib's seva has been happening from Satyug onwards ?