It hasn't and it won't; I've been doing it this way for about 5 years now and it works just fine. And it will continue to work just fine.
I'm not deceiving anyone; I really don't think that if my customer got invoice number 28763276 one week and invoice number 95377867 the next week that they would be deceived into thinking that I'd sent 66,614,591 other invoices inbetween.
Which is why I seed it with a random number generated by compositing the least significate bit from multiple analog port reads of a floating input (with time to drift between reads); you can read more about the technique I use here: https://rheingoldheavy.com/better-arduino-random-values/
Nobody "smelled any rats" because there were no "rats to smell".
First up, the accounting system would tell me. Second up, it's highly unlikely to ever happen (and it would take about 2 seconds to generate another one if it did) because I only send out around 200 invoices a year and an 8 digit number covers 100,000,000 possible numbers - so the chances of getting a duplicate are statistically highly improbable; about a 50% chance every 1/2 a million years.
Again, I'm not trying to impress - or deceiving - anyone. There is ZERO requirement for invoices to have sequential numbers; it is completely my decision as to what numbers I put on my invoices.
Apologies to the OP, but I felt compelled to respond to this.