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I completely respect and understand your interpretations of the rules as not being amended to address this.
However, thematically I think it makes sense to count an interdictor as a Star Destroyer for the following reasons: 1) it takes the same amount of damage to kill one; 2) they are important ships that will likely be even more protected by the Imperials; and 3) they are actually Star Destroyers.
I will probably play it that way in my games. YMMV.
The fact that you have already dealt the empire a serious blow by destroying a non-replaceable unit can be considered reward enough.