To receive ‘airplay’ and to sell the record in the shops Columbia released promotional or DJ copies. These were ‘not to be sold’ (and stamped with that remark), but now are widely sold on the internet and at record-markets. Some are very interesting, because they have MONO editions of the songs or even better a (slighty) different version of the lp version. We will take you these on this blog too. But here are a few examples of the promotional releases of ‘Bridge over troubled water’:
The mono version of Columbia 4-45079:
Remarkable is the large Blue A on the A-side. Both side are MONO versions.
The Stereo and Mono side of Columbia 4-45079:
Here is the STERO side clearly indicated by the green color of the label.
For ‘extreme’ colecftors it is also important to know which MATRIX was used, which could indicate a ‘very early version’. But we have to be carful here, becuase Columbia used different pressing-plants who all had their own MATRIX numbers.
JZSP 152907-2A and ZSP 152908-1B for the upper and
JZSS 152946-1C and ZSP 152079-2AA for the lower release.
Paul Simon - 'Time it was...it was' 
The business of different pressing plants handling this record is very real; the promo with both sides mono was pressed in Pitman, NJ whereas the mono/stereo promo was from Terre Haute, IN. My own mono/stereo promo copy of this record, however, is also from Pitman, with keyboardist Larry Knechtel’s name at an angle beneath S&G’s artist credit at left. Of course, the original stock release was mono.
I am interested to know how one can see the or know where a record was presses, in which plant. I must check if I have one with Larry Knechtel mentioned.
The A side of Terre Haute and Santa Maria pressings of the “BOTW” single all list Mr. Knechtel’s credit below the producers credit at the bottom, unlike the Pitman which had him angled below the artists name at left. So you’ll see him mentioned regardless of which pressing.
For what it’s worth, my preference is for the mono mix.