In this part of a series of mid-level Double Column Transposition challenges, the keys that has been used for both transposition are given. Find out from which phrases they have been derived!
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I'm sorry to be a pain in the *, but "SUCCESS" isn't 4,7,2,3,1,5,6 or DGBCAEF.
It is 4,7,1,2,3,5,6 or DGABCEF.

Success in understanding that

"SUCCESS" isn't 4,7,2,3,1,5,6

does not guarantee the success in solving this challenge, at least for me…
Is there some known method/algorithm or we have to improvise ourselves, or the problem is not as hard as it seems for me at the moment?

…it was the last option of my previous sentence

As usual, Bart is correct!.

Indeed, there is a mistake in the explanation (but fortunately not in the challenge itself):

The example should be:

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Suppose the word is "suggest". You arrange the letters in
alphabetical order and number them. For the same letter, the first
occurrence will be assigned a lower number than the second
occurrence, and so on.

E is the lowest, so its number will be 1.
G is the second lowest. So the first G will be given a number 2. For
the second G, we can't use again 2, so we will assign it 3.
S is the next lowest letter. There are two occurrences of S, they
will be assigned the numbers 4, 5.
The next letter in alphabetical order is T. I is assigned the number 6.
U is the highest letter. It is assigned 7.
So "suggest" translates to 4,7,2,3,1,5,6, and its literal equivalent DGBCAEF

Unfortunately, there is no well defined process to convert a
numeric/literal key back to its original phrase/expression/keyword.
Also, there can be several words and expressions which map to the
same key. For example, "runners", "ruppert" and
"luciano" all produce the same "DGBCAEF" key (which was
derived from "suggest").

It is advised to use the following link to check your conversion:

http://rumkin.com/tools/cipher/coltrans-double.php

Select the option: "Key Word(s) - Duplicates numbered forwards" (instead of "Numeric Key - Spaced Numbers")
type in the word or sentence (no space), and the numeric equivalent is displayed below).

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Bart, thank you for your sharp eye, do not hesitate to point out any mistake, even if only in the examples.

George (the author)

I am stuck on this for a long time now. Is this a hard one or is there a fundamental algorithm or approach that I am not aware of. Any hints would be appreciated!