There is a lot more to why most automotive chips do not use the most advanced generation of Si technology than testing and reliability. Yes testing does add a few months to the new product cycle but there are several other reasons. The vehicle design cycle is multiple years and adds much more than testing adds. Legacy ICE automakers typically have a three year development cycle. In addition, most semiconductor companies sale their chips to Tier 1 automotive module suppliers like Continental, Bosch, Harmon, Panasonic, Denso, ... etc. Their development cycle will add another 6 months or year to the development cycle.Cars will never be on current generation "chips" due to the stringent testing protocols required for use in what is essentially a 2 ton deadly weapon.
In addition, there are only a few automotive functions like CPUs and image processors that can take advantage of the latest semiconductor technology from a power and computational performance point of view. Functions like ADAS image processing, instrument clusters and infotainment use more advance semiconductor technology than other functions. The most important reason is that the majority of automotive semiconductors are analog circuits that interact with either people or the environment. The most advanced semiconductor technologies are not capable or cost effective in these applications. Applications like radar, sensors, engine control, transmission control, airbags, chassis and body control, braking, steering assist, traction control, etc.
Automotive companies do not change their orders on a monthly basis but they do not have the same long term contracts that companies like Apple and Samsung will have. When the COVID occurred last year, automotive companies drastically cut their orders as they idled factories. At the same time people started working from home creating demand for home office and home automation products. These companies did take the semiconductor capacity that the automotive companies had before. While automotive capacity has been increasing in 2021 a couple of natural events have continued to limit supply. The February winter storm in Texas took many wafer fabs (Samsung, NXP, TI, AMD, etc.) out of commission for several months. The recent flooding in Germany took out a primary copper supplier that is used in automotive semiconductor packaging.
As far as counting semiconductor content in cars, most people in the industry use dollar value instead of number of units. The picture below is a Continental traction control module. Is it one semiconductor or 100 for all of the components? Electrification and autonomous driving are the two biggest growth areas for semiconductors.