Wisconsin has a six-year retention period. So, this may fall just outside of that period. However, it's still quite possible that the Attorney has retained this record. It's certainly worthwhile asking for another copy - on the basis that you lost yours.
Most attorneys would probably still have it. If the trust is still active (has funds and has not been terminated) I am sure someone has a copy, but perhaps its a bank or another attorney.
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I agree with my colleagues. Most attorneys will still have at least an electronic copy of the trust saved in their electronic files, even though it is not required due to the retention period having expired. The trustee, if not a bank or other attorney, will likely have a copy.
My responses are of a general nature and not having the opportunity to get all of the background may mean that they are not complete. I may not be a licensed attorney in the jurisdiction where you are seeking advice and is based solely on the laws and my expertise in those states in which I am licensed. Therefore, this advice can provide a good foundation in seeking quality legal advice in your particular area.