This is the account that occurs to me so far as valid.
An initial 1-2 and a particularly long correction WXY, which would be ending in the last 5.
Alternatively: (in gray) the second hump can also be counted as 1-2 (I have a hard time finding evidence for one or the other). It would also be finishing with the last 5 and it would be the beginning of 3 of 3.
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