Zimbabwe 2nd Dollar Bearer Checks, 10 Million dollars: P-55a vs P-55b

[Revenant]

PMG has certified some 10 Million dollar Zimbabwean Bearer Checks as P-55a and P-55b. I can't find anything in my available references that explains what the difference is between the two. Most other PMG notes have some kind of notation on them which indicates why a note is the sub-type it is. For instance: P-5a will say "light brown back," where P-5b will say "dark brown back." I can't find anything like that on these notes. I know the 10,000 and 100,000 notes in the same series have a difference in the digit grouping that sets P-46a and P-48a apart from P-46b and P-48b, but that doesn't seem to impact P-55.

Could someone explain what the difference is between these two types?

[Jennifer F.]

Good afternoon. Thanks for your message.  After review, it appears that the difference between 55a and 55b would be the series.  55a would be series A and 55b would be series D.  If you have any other questions, please let us know.  Thank you!