Here is why people think there is double counting...
I joined SPG in 2015 and have over 250 lifetime nights.
2015 - Plat This is the first Plat qualification which was for 2016 but the poster got to enjoy benefits immediately.
2016 - Plat This is the second Plat qualification which was for 2017.
2017 - Plat This is the third Plat qualification which was for 2018.
2018 - Gold This will be the fourth qualification year (three Plat plus one Gold) which will be for 2019.
2019 - I am on my way to qualify for gold (this year I've stayed 17 nights already but have other trips planned which would comfortably get me over the 25 needed) This is the year mentioned above, not an additional year. This is the same year mentioned on the 2018 line.
If the poster also qualified for elite status in MR he could hit another credited year before the end of 2018. But as it is outlined in the original post, the poster would only have four years by the end of this year, not five.