Backtesting with MT4

Trading Systems Expert Advisors and Automated Trading
1

Hello guys.
I dowloaded the data for each pair that I backtested with my EA from Historical Center (MT4).

I backtested it from September 2017 to September 2018 and the results were good.
I tried to backtest it from 2008 and from 2010 and the results were bad.

What is the issue?

  1. The strategy didn’t work in past
  2. MT4 Data weren’t good
  3. Both :smiley:

Can someone help me to have accurate results to understand if this EA is good or not?
Do have I to test it with demo account for 3-6 months and leave out the backtesting?

Thanks in advance!