rare vintage 60's/70's adjustable length watermelon cardboard crossbody bag

i bought this precious bag at a vintage shop a few years back and have only worn it a few times, so i'm hoping someone out there will get more use out of it! i was told it was from the 60's/70's but have never seen another like it anywhere, so i'm not 100% sure. it's made of laminated/plastic-coated cardboard so it's hard-sided and pretty sturdy-- i'd say water-resistant but not waterproof because there's some of the plastic is peeling near the bottom due to age. it could probably be resealed. aside from that and a bit of rusting on the metal bits, the bag is in fantastic shape-- i've included photos of the imperfections. approximate measurements: length: 15.5" height: 8" depth: 3.5" feel free to ask any questions or request more photos! xx