The encoder used in that breakout is not an absolute encoder; it has no way of determining when it is at a home or 0 position. Even if you modify the code on the breakout board to save the position, there is no way to detect whether it has been turned while the power is off.
When powered up, it keeps track of the position (calling where it was at powerup “0”) in firmware . Looking at the datasheet for the encoder (located on the “documents” tab), the part used is a quadrature encoder, so there is no way to know what happens when power is off. I have added a comment to the product page.
/mike
(BTW, I have no connection with SparkFun other than a customer…)