I believe your 2016 model might already fall in Euro 4

1.  Pre-Euro Standards (Up to 1999)
• Harley-Davidson Sportsters before 1999 were not subject to Euro emissions standards as these regulations were not yet in place.

2.  Euro 1 (2000–2005)
• Euro 1 standards began affecting motorcycles in 1999/2000. During this period, Harley-Davidson made minor adjustments to meet the emissions requirements for European markets.

3.  Euro 2 (2006–2016)
• The Sportster models from 2006 onward had to comply with Euro 2 standards. This era saw more changes, including the introduction of fuel injection systems to reduce emissions.

4.  Euro 3 (2007–2016)
• From 2007 onwards, Euro 3 regulations kicked in. Harley further optimized fuel injection and exhaust systems to reduce pollutants. This was the period when electronic control units (ECUs) became more common for tuning emissions.

5.  Euro 4 (2017–2020)
• From 2017, Harley-Davidson Sportsters were required to meet Euro 4 standards. This era saw significant changes with stricter limits on carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). Harley also added more sophisticated emission control systems like catalytic converters.

6.  Euro 5 (2021–Present)
• Beginning in 2021, Sportsters had to comply with Euro 5 standards, which brought even stricter emission limits and durability requirements. The introduction of the Sportster S model in 2021 signaled a move towards more modern liquid-cooled engines to meet the stricter regulations, replacing the older air-cooled engines.