Probably a summer student hired at Fram came in for work one morning hung over and when spinning the Trodat 'Made in Canada' stamp to correct 2946389 number for that days' assignment of stamping the bases, let it stop at at a 6 instead of a 9.....thats all.
Hopefully yours is the only one he did that way before waking up.
Same kid likely did this one too, all backward numbered on a 340 shaker base