Computer tape quantities in the 70's or 80's?

Bitsavers has preserved a couple of key marketing studies that help me understand the wide world of disk storage in the 70's and 80's. For example http://www.bitsavers.org/pdf/dec/competitiveAnalysis/Engineering_Strategy_R… has numbers both for DEC and world disk market. DEC sales were a substantial chunk of the world market of disk sales and the document seems to understand the up and coming world of small disks while also having good numbers on the mainframe disk world. I wonder if we have any documentation (probably internal numbers but maybe also including guessing at competition) of, say, reels of half inch magtape sales sold in the past. Chances are this would be a 3M or competitor's document since the bulk of magtape media sales were not normally done through DEC or IBM etc. For example I might guess that by the 1980's there were 5 reels of 2400foot half inch magtape for every person in America and tapes were reused up to 10 years. That would imply that 100 million reels of tape were sold a year. But that's just a guess and maybe I'm off by an order of magnitude one way or the other. So if you know of any documents to help me get a comprehension of the scale of computer tape manufacturing in the 1970's and 1980's, please let me know! It might be a 3M press release bragging about opening a new plant and what it's capable of, for example. Tim N3QE