Drivetrain is always limited during events (Asphalt myth)

The claim that Drivetrain cards are always limited during events in Asphalt 8 is a special case of the common belief that the game grants less of the cards needed to upgrade an event vehicle.

Assumption
Especially during events, players are focused on obtaining Pro Kit cards for the vehicle offered by the event. As the majority of vehicles are speed based, the most useful cards are Drivetrain (increasing top speed and acceleration) and Tires (increasing top speed and handling). There have been several reports of players not obtaining Drivetrain cards during an event, so it is possible that there is a coresponding mechanism in the game that decreases the frequency of Drivetrain cards needed by an event vehicle.

Test
To verify this, a valid method would be to oberve the relative frequency of Drivetrain cards during a longer period that includes phases both with and without events.

As a sample for this test, the database of WikiProject Statistics has been evaluated from the start of the Fast Lane Update until the end of the 2019 Spring Update. The observed Pro Kit Boxes were Daily Kit Box, Engine Box, Extra Box, Finish Line Box, Multiplayer Pro Box, Optimal Shuffle Box, Optimal Split Box, Random Box, Starter Box, Tech Box, and Ultra Box which are the most common boxes.

Dedicated Parts boxes like the were not included because there was no statistical data available for this period.

If the assumption was true, the relative frequency of Drivetrain cards during events should be significantly lower than during periods without events.

Results
As there aren't many periods without events in Asphalt 8, the corresponding sample size is smaller, but still large enough for the law of large numbers to minimize the effects of outliers. To make the results comparable, the table also lists the corresponding relative frequencies.

For all classes, the relative frequencies of Drivetrain cards during event and no-event periods are extremely similar.
 * The total of all classes differs only by 0.79 % which is less than 1 card out of 100. This is within the normal range of deviations during random processes.
 * There is a tendency of no-event periods granting slightly more Drivetrain cards than event periods for class D to A, but the differences only range from 0.09 % (less than 1 card out of 1,000) to 0.79 % (less than 1 out of 100).
 * The relative frequency of Class S Drivetrain cards is even higher during events, but also only by 0.99 %.

There are no significant differences between no-event and event periods.

Conclusion
There is no mechanism that decreases the frequency of Drivetrain cards during events. The assumption is wrong.

This doesn't refute the observations of some players who observed a long streak of getting no Drivetrain at all. As the Pro Kit Box process is random, it is possible (though less probable) that a no-Drivetrain streak occurs. There is no guarantee that


 * a streak of no Drivetrains will immediately be "balanced" by an increased number of Drivetrain drops ("gambler's fallacy")
 * a small number of observations will coincide with official drop rates (=expected values).