Hi,
what is the difference between the -a and -b entries for Colombia's 2 000 Pesos P# 439?
On banknotes that I have, I notice different coloration for different years, mainly visible as orange color on the ground portion of the painting (reverse) and on the right side of the numeral “2” printed on the left corner of the same side, much similar to the colors on previous years that had the Pesos Oro denomination (P#430, P#433a). On the comments for one note of these, it is stated that the difference in letter is due to different printing companies, while the other doesn't specify (what is Aa vs Ab).
I hope this photo helps explain what I mean.

All 3 notes are P439, and from top to bottom, they are issued on:
17-Dic-1994
1-Nov-1994
1-Jul-1993
As can be seen in the photo, the printer is the same for all.
Any and all comments are greatly appreciated.