Anyone familiar with this mag card holder?

[mfleming]

Here's an interesting recent find from an HP41 manual collection I picked up on TAS. Tucked in amongst the QRC's and overlays were two of these HP-65 Pocket Instruction Cards. Here are a couple of pictures, back and front sides, with and without magnetic cards.

       

I've never seen a photo or reference to one of these before, so it was a pleasant surprise to find them. They appear to be a three layer construction, cardstock printed front and back with a thinner spacer layer in between to provide room for inserting a magnetic card. It's likely that adhesive was applied to both sides of the spacer before affixing the outer layers. Note the notch in the card space opening to ease entry of the mag card.

I wish I had more of these because they look like a handy way to keep frequently used cards around and to document your own program cards. Anyone know how common these were "back in the day" when the 65/67/41 card readers were common? I wouldn't mind duplicating a shoebox full of these!

~Mark