Subject: Are the lymphocytes in the lymphatic system included in the WBC count?

Please help me understand briefly how lymphocytes "travel" from the blood 
system to the lymphatic system and back to the blood system.  I believe the 
transition takes place at the capillaries and interstitial fluid level.  I was 
told that the lymphocytes go back to the blood system from the lymphatic 
system at the superior and inferior vena cava.  Is there a particular vessel 
where lymphocytes leaves the blood system and enter the lymphatic system?  

I understand that the normal WBC count from a blood test is about 4,500 to 
10,000 per cu mm.  I was told by my teacher that the lymphocytes in the 
lymphatic system are not included in the count.  Theoretically, it sounds 
right because we only count the lymphocytes and the other four types of 
leukocytes in the blood system.  But the truth is the lymphocytes do travel 
back to the blood system (for oxygen?) from time to time.  How can they not be 
included in a blood test?  I guess since the lymphocyte count in the lymphatic 
system is minimal and the normal WBC range is so wide, it doesn't make much 
difference.  However, I just have to say something when I am not sure about 
what I heard.  I appreciate your shedding some light to this.

Re: Are the lymphocytes in the lymphatic system included in the WBC count?