There is a difference between bottle cap screw threads and other threaded nut-style connections. Bottle cap threads have separate specifications which have been described and linked to elsewhere here.
The Gardena hose fitting you scratched off uses standard V-profile threads. They are produced two different ways:
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A continuous threaded tool insert with electrical actuator to unscrew in tool prior to ejection. This is very expensive, slow, requires maintenance, but produces very accurate, fine threads.
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Tool halves are machined separately with half diameter thread and the part ejects normally. This requires some careful tool machining to ensure the thread halves align, but is no problem for competent tool shops. These parts of course mold cycle very fast but will show occasional part - part thread unevenness due to process variance over time, tool wear, or flash. Looking carefully at the Gardena hose fitting you can see the tool witness line across the thread V profile, this part was molded from separate half-threaded tool cavities.
General rule for thread engagement like you illustrate is .5 - 1X thread pitch engagement minimum, i.e. 1-16 UN thread should engage between 8 - 16 full threads . Of course you know threads work via competing tension and compression force, therefore the more thread surface engagement your parts have the stronger, better seal, they will be when engaged. Also, as material thickness is different in the thread area, you must be very careful with geometry in the thread relief - neck area to prevent typical plastic molding phenomena.