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With addenda, you should also discuss whether the material you will be working with is the same or different from that in the original collection. Is it the next 10 years of board binders? Is it A/V that was not donated before? Does it come from a different office of the organization or the attic of a board member?
When adding addenda, it is important to write a sentence or more in the top-level scope note articulating what you are doing and why. If you are doing a lot of renumbering, this can get kind of complicated. Writing this out in the processing plan can help clarify what the work is (you may want to complete the rest of the processing plan and then write this statement.)
EXAMPLE:
Appraisal and research strengths:
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