This is not surprising considering you're underage. Most men stop growing at 16, some continue to grow a little until 18 and very few (less than 1%) grow at 19-21. Growth at 21-25 is extremely rare.
The problem with measurements at home is that you probably don't remember at what time during the day you measured yourself 8 months ago.
If the recent measurement you took was in the morning or within 3-5 hours of waking up and the one 8 months ago was say in the afternoon or at night, those 2cm of height are almost definitely due to height variance during the day.
Our spine and cartilage compresses during the day due to gravity. Most people shrink around 2cm (3/4") by the end of the day and no, it has nothing to do with posture. So for example if you wake up and immediately measure yourself at 172cm, you'll be around 170cm in the afternoon or at night depending on physical activity.
We all have our "maximum" (right out of bed) and "absolute low" height. I personally shrink around 2cm on average, but on the days I walk a lot and do heavy physical work I can shrink up to 3cm.
If you want to track height, it's always best to measure right out of bed and I'm talking within a couple of minutes of waking up in the morning, preferably immediately. This way you can easily tell you're growing because if you're not you'll always wake up at the exact same height, but during the day your height can vary depending on physical activity and time of day so it's not a good idea to measure during the day.
Personally I'd notice 2cm of growth without even measuring, but I've been a little obsessed with height ever since I was 18.
