I have a lot of old family negatives from the 80s and 90s that have a strip of paper thoroughly stuck to the top. Why was this done, and is there a safe way to remove it?
The paper strip was applied by the photofinisher as they were using high-speed color printer machine. The paper interacts with the film feed mechanism of the printer. The paper interacts with the film frame cutting machine that cuts the film into strips without cutting into an image frame. It is only applied to the edge of the film thus it does no harm. If you feel you must, you can trim the paper with scissors down to the edge of film. I can think of no reason to remove the paper portion that is adhered to the film with glue.
Posting this as an answer, but use this information at your own risk as I've never tried this! I would try PEC-12 – it's a photographic emulsion cleaner. Read the FAQ online. I've never seen these strips glued to negatives like that.
PEC-12 is designed to remove non-water based stains, grease and inks from photographic emulsions and bases. It removes finger oils, grease pencil, adhesive tape residues, mildew, smoke and soot damage, gold foil stamp and most ball-point and permanent inks. It will aid in the removal of firmly affixed adhesive tape.