Normal tolerances for marble production are not that tight. The 1.5 mm difference between the largest and smallest you describe amounts to about 6/100". Vintage American marbles had tolerances of about 1/16", e.g., a No. 0 marble (nominally 5/8") was anywhere from a hair over 9/16" to 5/8", while a No. 1 marble would be anywhere from a hair over 5/8" to 11/16", etc.
And FWIW, I think the peewees you're showing may be JABOs.