My guess.....
A new Grand master decided the old regalia needed to be replaced with new. They were after long deliberation obtained and the old ones were stored in the attic and after the old men died, were forgotten.
The old ones were after all, merely homemade and lacked the prestige of that which is new and made by the foremost creator of regalia.
I suspect that your guess is correct. But who stuffed them in between the insulation? It has been my experience that lodge and fraternal regalia is expensive and is generally treated with great respect. But, my mother bought me a KC sword in a junk shop one time. She thought it would make a good wall decoration. (She’s not Catholic.) In the first place it could not be hung because one of the brackets was missing. In the 2nd place, I am Catholic and I did not want to display it in my home. It stood around in a corner of my closet for 15 years, falling on my foot every time it was bumped. When we were moving, my husband finally gave it to another junk dealer who was Catholic. He was delighted and promised to return it to his own KC lodge for proper disposal. Of course, he may have lied about his intentions, too. After all, he was a junk dealer, and that is part of the business model.