I'm guessing that's what it refers to.....seems about right for a typical road tire like a 23-25 mm, 35 mm may be pushing the limit for a narrow rim. What's the external width of the rim? I have a friend who used to study all the various tires and effects of differing rim widths, effects of inflation, etc....even had a website for a while dedicated to it, too. While he was more geared towards mountain bikes then but he's also a big road biker....think I'll ask him what he thinks.
Here's another reference about various tire sizes and rim designations
https://www.sheldonbrown.com/tire-sizing.html
70psi sounds on the high side for a 35mm tire, what is the max inflation pressure indicated on the tire?
Did you ever look at the tubes to see how they were blowing? You aren't tubeless, are you?