I found it easy to do, for several purposes I have kept a spreadsheet of dates that I fly for about 20 years. Also about 15 years ago I put together a list of where when I had flown in the previous 15 years, So it was not too daunting to do, the detail is not down to exact flight numbers and depature times, but it is pretty comprehensive for the last 30years, only those before that are a bit more hazy.......