There was a sect called Raamdaas but Guru Sahib has redefined the real Raamdaas by calling them Sat-Raamdaas. The details of Sat Raamdaas are in the 6th Pauri of 9th Ashtpadi of Siri Sukhmani Sahib:
ਜਿਸ ਕੈ ਮਨਿ ਪਾਰਬ੍ਰਹਮ ਕਾ ਨਿਵਾਸੁ ॥
ਤਿਸ ਕਾ ਨਾਮੁ ਸਤਿ ਰਾਮਦਾਸੁ ॥
ਆਤਮ ਰਾਮੁ ਤਿਸੁ ਨਦਰੀ ਆਇਆ ॥
ਦਾਸ ਦਸੰਤਣ ਭਾਇ ਤਿਨਿ ਪਾਇਆ ॥
ਸਦਾ ਨਿਕਟਿ ਨਿਕਟਿ ਹਰਿ ਜਾਨੁ ॥
ਸੋ ਦਾਸੁ ਦਰਗਹ ਪਰਵਾਨੁ ॥
ਅਪੁਨੇ ਦਾਸ ਕਉ ਆਪਿ ਕਿਰਪਾ ਕਰੈ ॥
ਤਿਸੁ ਦਾਸ ਕਉ ਸਭ ਸੋਝੀ ਪਰੈ ॥
ਸਗਲ ਸੰਗਿ ਆਤਮ ਉਦਾਸੁ ॥
ਐਸੀ ਜੁਗਤਿ ਨਾਨਕ ਰਾਮਦਾਸੁ ॥੬॥
Basically Guru Sahib is explaining that such Gurmukh whose mind Parbraham Vaheguru resides he is the real Raamdaas. Then in the next 8 Pankitis Guru Sahib has explained the characteristics of a Raamdaas i.e. an accomplished Gurmukh as follows:
1) He has viewed Aatam Raam i.e. Vaheguru with his own eyes.
2) He has attained the nature of being servant to all.
3) He considers Vaheguru to be extremely (Nikat Nikat) and this way he gets accepted at the Dargah of Vaheguru.
4) Vaheguru Himself does Kirpa on His servant and such servant realizes everything.
5) Gurmukh Raamdaas stays with everyone but from within he is aloof from all; such is the way of Raamdaas.
Gurbani is Agam Agaadh Bodh. Raamdaas is a term Guru Sahib has used from Gurmukhs just like Aparas, Baishno, Bhagauti, Pandit and Jeevan Mukat etc. in this 9th Ashtpadi. All these were different sects of that time and Guru Sahib has redefined them in the mould of Sikhi. These are not different stages of spirituality.
Kulbir Singh
ਸਤਿਗੁਰਬਚਨਕਮਾਵਣੇਸਚਾਏਹੁਵੀਚਾਰੁ॥