Power pivot Calculate Running total column using ALLEXCEPT

Hello?

Work book attached .
Can someone help with this; I've created running total column using
Using AND

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but have the same result using ALLEXCEPT which cut things down, but I'm not really sure why it works? can someone explain a bit

Using Xcept

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Also is it possible to MAX rather than EARLIER in Calculated column , I know using EARLIER in a measure isn't that easy.

Richard.