

Or just start the cut in the long direction and slip the knife between the top and bottom flaps for the sides. Assuming whoever taped it didn’t add more tape perpendicular to the main length, though even then you just need to start a cut for each of them. Tip just needs to barely pierce it.
We are closer to the 2060s than the 1960s.
This year, 1975 is as far away as 2075.