The regex commented.

my( $authors, $title, $thing, $pub, $date, $comment, $no ) = m/
    ^
    ## Author(s): Capture the minimum needed to satisfy that:
    ##    a) It ends with a '. '
    ##  b) And the next word is not an initial 
    ##        IE: Lookahead and check the next word starts with  
    ##         1 uppercase *and* one lowercase character.
    -( .*? \. ) \s(?=[A-Z][a-z])
    
    ## Title: Greedily capture something that ends with '. '
    ( .+ ) \.\s+
    
    ## Location: Non-greedily capture
    ## Ends with a ': '. 
    ## Doesn't contain a ':'
    ( [^:]+? ) : \s+
    
    ## Publisher: 
    ## Single word followed by a ', '
    (\S+), \s+
    
    ## Year: Capture Four digits
    ## Discard anything else upto '. '    
    ( \d{4} ) [^.]* \. \s+
    
    ## Comment: Greedy capture non-'[' characters
    ##  Ie. Stop capturing when you see a '['
    ( [^\[]+ )
    
    ## No: Capture 1 (or more) digits between '['  & ']'
    ## Discard any trailing space to the EOS.
    \[ ( \d+ ) \] \s* $
/x;
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