Is lo (咯) valid pinyin?
Definition

According to yabla, 'Io' is a valid pinyin.
Quoting yabla:


  咯 
  luò
  
  
  
  to cough up
  
  
  
  
    咯 
    lo
    
    
    
    (final particle similar to 了, indicating that sth is obvious)
    
    
  
  
  咯 
  gē
  
  
  
  (phonetic)


Usage

Example Usage just for that middle one(from yabla):

哟呵呵呵我们回来咯回来了回来了

yohēhēāwǒmenhuílailohuílailehuílaile

English:
Ha ha ha ha! We are back. -You are back. You are back.

Sidenotes

A pinyin table from allsetlearning:



That proves to me that lo is a valid pinyin.