In the Soviet Union, everything was regulated by rules, including the names of the cars produced by Soviet manufacturers. The Government imposed a system to name all vehicles using a numeric code.
The Soviet vehicle numbering system was simple in the early decades, but it became a little more complex by the mid-1970s. The advantage for manufacturers was that they did not have to rely on imagination each time they rolled out a new vehicle.
A Standardized System That Had to Be Used by Law
Designing a car takes a long time. Brands must consider many things from the moment they sketch a new model to its market launch, including coming up with a name.
Although it might not appear so, it is a very tricky task. Each brand has its own style, and some are quite distinctive, such as SEAT, which tends to use names of Spanish localities for its cars. Others revive names of iconic models for new cars that have nothing to do with them; some make it so complicated that it becomes difficult to understand, and certain models should simply change their name.
No es algo que se suela dejar al azar, hay equipos de personas que trabajan duro para dar con el nombre perfecto y el marketing es crucial en este proceso. Lógicamente, ahora es más complicado que antes porque muchos nombres ya están cogidos y, sobre todo, porque las marcas tienen gamas mucho más amplias. Cuando solo había dos coches en el catálogo, era más fácil elegir nombre.
Por supuesto, es algo que depende de cada fabricante: algunos se complican más la vida y otros prefieren hacer las cosas de forma más sencilla. También hay casos en los que la imaginación no es posible, como el de las marcas de la vieja Unión Soviética.
In 1945, the Soviet Government decided to implement a rule requiring vehicles produced by Soviet manufacturers to be identified with a standardized, numbers-based system.

Moskovitch with the old Soviet vehicle-numbering system. The USSR assigned the number range from 400 to 450 to MZMA, the factory that produced Moskvitch.
This system allocated a range of numbers to each brand, and manufacturers chose a number from that range to name their cars. For example, GAZ had the range 1 to 99, ZIL 100 to 199, and KAZ 600 to 649. For buses, one would pick a number from 650 to 699, and for trucks from 700 to 999. Some models named under this system remained in production into the early 2000s, such as the LAZ 695 bus.
As a rule, manufacturers had to adhere to this system until the mid-1970s, when it was replaced by the modern Soviet vehicle-numbering system.
This new system was a bit more intricate than the first. Each name had to be composed of four digits, but could have up to six; the first digit depended on engine displacement for cars, on weight for trucks, and on length for buses. The fifth and sixth digits were optional.

Lada 2104: the 2 because its engine is between 1.1 and 1.79 liters, the 1 because it is a passenger car, the 04 because it is Lada’s serial number.
For cars, the 1 was for models up to 1.09 liters of displacement, the 2 for engines between 1.1 and 1.79 liters, the 3 for engines between 1.8 and 3.49 liters, and the 4 for cars with more than 3.5 liters.
For trucks, the 1 was reserved for those weighing up to 1,200 kg, the 2 for those weighing between 1,200 kg and 2,000 kg, and so on up to 7, which was used for those weighing more than 40,000 kg.
In the case of buses, the first digit of their name started at 2 for those up to 5 meters long, the 3 was for those between 6.0 meters and 7.5 meters, and so on up to 6 for those longer than 16.0 meters.

Kamaz 5320. The 5 is because it is a truck with a gross weight between 14,000 and 20,000 kg, the 3 because it is a truck, the 20 is Kamaz’s serial number.
The second digit of the name referred to the vehicle type: 1 for cars, 2 for buses and vans, 3 for trucks, 4 for trucks with semi-trailers, 5 for dump trucks, 6 for trucks with trailers, 7 for vans, 8 for reserved vehicles, and 9 for special vehicles.
Finally, the third and fourth digits referred to the model number produced by each factory, i.e., the sixth model manufactured by a given brand or the fifteenth model produced at a plant.
Optionally, manufacturers could use a fifth digit to specify different versions or modifications of the same model. And it could get even more complicated with a sixth digit to specify option packages.

Kavz 4270. The 4 is because it is a bus measuring between 8 and 9.5 meters in length, the 2 because it is a bus, the 70 is Kavz’s serial number.
With an example, the system becomes clearer: the Moskvitch 2140 was a car with a 1,500 cc engine, so its first digit is 2, the range used for passenger cars with engines between 1,100 cc and 1,799 cc. Its second digit, 1, indicated it was a passenger car. Since it was the 40th car Moskvitch produced, its third and fourth digits are 4 and 0.
Clearly, it was a very complicated system. In the Soviet Union, manufacturers had to use it, but when exporting a car it was not required, so it was common for exports to bear a different name outside the Soviet Union. Of course, brands did not complicate matters; for example, the Moskvitch 2140 from the previous example was sold outside the Soviet Union as the Moskvitch 1500 because it had a 1,500 cc engine.

Spain’s technical sheet for a Lada Niva (VAZ 2121).
That said, in the vehicle documentation the name was always shown according to the Soviet system. Therefore, the Lada Niva available in Spain was also called VAZ 2121, which is how it was known in the Soviet Union. If you own a Lada Niva, you can verify this by looking at its technical sheet.
In any case, whether convoluted or not, it is the system that car brands in the Soviet Union used for years, even after the dissolution of the Soviet Union. What is clear is that this system prevented manufacturers from letting their imagination run wild, as happened with Mazda Laputa, Nissan Moco, or Mitsubishi Pajero.