When making an unchained monk only monk levels are accounted for in showing the number of attacks for a flurry of blows. Thus if one already has iterative attacks but only due to other classes, they do not show in the flurry of blows until one would have the iterative attacks in the unchained monk class.
In the example i am providing a character at level 7 has attained +6/+1 BAB but only due to 3 levels in the rogue class, while the unchained monk class is at level 4. Thus only 2 levels later (at level 6 of the unchained monk class) the iterative attacks are shown properly in the flurry of blows.
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