The post-war Soviet aircraft industry was saddled with ridiculously convoluted Construction Number schemes in order to defeat such analysis. They varied by type, model and factory.
Here's an example for one model built in one particular factory:
All start with 353 plus three more digits which indicate the sub-type (242=Mi-24V, 246=Mi-24D etc) The seventh digit seems to represent the quarter built while the eighth digit seems to represent the year built. The last five digits as the famous post 1974 random nonsense number.
They only abandoned the schemes in the early 1990s.
Does not follow. Only follows if:
- PKs are sequential
- and PKs are non-zero non-negative
- and they have not been reset at any point (or the sequence generation otherwise modified)
- and all preceding PKs are those of customers (as opposed to test values, invalid PKs due to a sequence number that was generated but the registration did not complete, or customers who have since left the service)
If PKs are sequential and natural and the sequence has not been modified, then you know there are no more than 1992 customers. Not exactly 1992.