Thank you all for your input, I assume many won't give a sh*t about this whole matter, but it matters to ME. I love consistancy, the same reason e.g. we consider 144,000 NOT literal because the rest of the surrounding verses (and Revelation in general) is symbolic. You can't have it both ways, right?
By that SAME rule, we agree that 7 times, or 2520 years, need to be counted as Jewish years. That would lead us, as the OP concluded, to 1886 AD instead of 1914 AD, a difference of 28 years.
But if we count 70 years as Jewish years, that would still bring us to a total of 70 years. The difference between using the Jewish and Gregorian calender would be 350 days, which is almost a full Jewish year of 360, but still wouldn't count as one, right?.
That difference however, when put under scrutiny, would be of influence when considering shorter periods of, let's say months, during those critical events. When it comes to history and calculations, details matter, right? It's not that I doubt historical science, but I'm just not aware of the "proper" use of 70 Jewish years in calculations by all oposing parties.