Can a person get into any stage of enlightenment without being aware of it? In Buddhism we classically have four stages of enlightenment:


Stream-enterer (Sotapanna);
Once-returner (Sakadagami);
Non-returner (Anāgāmi);
Arahant.


My question, as stated in the title, is: can a person attain to any one of the four stages mentioned above without clearly recognizing it?
Samyutta Nikaya - Maha Vaggo (2) Sotapatti Samyuttaya 


Here you can find sutta where Buddha explains who a Sotapatti stream winner is. 


Unwavering impression of Buddha 
Unwavering impression of Dhamma 
Unwavering impression of Sangha 
Maintains Aryakäntha sîla 


There are other places in Tipitaka where Buddha mentions the first three and the fourth one as 


No doubt of The Four Noble Truths (Sammä Ditti) - 


A definitive answer may be found here: 


  Samyutta Nikaya - Maha Vaggo (2) Sotapatti Samyuttaya - 11.1.5


As you might notice, as long as there is doubt (Vicikiccä) you are not sothäpanna. By observing your own mind, you can confirm if you are sothäpanna or not. 

To go a step further, it is wise to practice Buddhism with the thoughts 


As long as I make assumptions using "me", "mine", "my soul" I need to practice detachment. 
As long as I have craving, anger or delusion, I will practice detachment, metta and vipassana (Sammä Ditti) 


This way, one won't waste time thinking am I this, am I that. Where there is craving, anger, delusion, there is harm for oneself and others. Therefore, you can practice this just by deciding to be harmless. 



 English Version