Intro:
Looking at covid19.rs/homepage-english/ I can see that there was a total of 1.444.532 people tested and the data is marked for 10.01.2022 at 15:00.
From the dataset:
Date: 2021-12-16, new tests: 13690.0, total tests: 7032035.0
Date: 2021-12-22, new tests: 14808.0, total tests: 7107851.0
Date: 2021-12-26, new tests: 9265.0, total tests: 7158932.0
As We can see Djoko's "ID" (7371999) is much larger than total number of tests for 26th of December 2021 (by 213067) and for me this furthers your point that We don't know how this number is generated.
(It seems to be sequential, but is it?)
This is exactly the same as here: https://ourworldindata.org/coronavirus/country/serbia
So I'm assuming that this dataset can be trusted.
The point:
From the dataset: Date: 2021-12-16, new tests: 13690.0, total tests: 7032035.0 Date: 2021-12-22, new tests: 14808.0, total tests: 7107851.0 Date: 2021-12-26, new tests: 9265.0, total tests: 7158932.0
As We can see Djoko's "ID" (7371999) is much larger than total number of tests for 26th of December 2021 (by 213067) and for me this furthers your point that We don't know how this number is generated. (It seems to be sequential, but is it?)