They specifically say lines/millimeter. I don't think that is a typo across many MTF charts. You need to spend a little time with Roger Ciclala's MTF charts, There are very few lenses that get out of the mud at 60 lp/mm. and then usually only in the center. Here are some examples https://www.lensrentals.com/blog/2019/10/more-ultra-high-resolution-mtf-experiments/ . Note that Roger normally only tests to 50 lp/mm and this was a far out special case test.They mean line pairs. It’s assumed, they don’t have to say it.