I used Hasselblad 1600 copy Kiev 88 with old sort of films and may be another 1 million used them , their film backs havent got even an red window and you can touch the backing paper and yes , for your all single advance , you must open the small window and calibrate the advance. There is no light leak , may be an roll waited in high humidify refrigirator or high heat or not fresh film including these cheap films make the backing paper numbers ink dissolve and impregnate in to the paper and make a semi transparent material like polymer reinforced glass.
I think you may be right. Since the markings and numbers are evenly the same 'exposure' on the negative, I'm thinking the ink rubbed off onto the emulsion. Also the numbers aren't reversed if that makes a difference