yes it does bunch up at the beginning, doing it carefully it will not bunch up as much, first rewind on another empty spool or advance in a hassy back, starting from exposed end start respool on 620 spool close to the 120 spool to catch the untaped end or palace a small piece of tape to hold it down,remove the tape and retape to flatten out the film its up about 1/8 to 1/4 inch tops
if you have an old expired film practice in the daylight, I've been doing it since 1967.