Here's not fun story about taxes in Spain: Once, I forgot to make a quarterly income tax payment to the Spanish Tax Agency (Agencia Tributaria). They waited until I was four months in default before informing me that I had not paid.

I had given them permission to deduct the amount from a specific bank account. However, I didn't have enough money in that account, so the charge failed. Since they were supposed to take it out themselves, one would think they should know instantly and notify me accordingly. But unfortunately, this was not the case...

Being four months in default meant they could fine me between 10% and 20%, plus interest, on the outstanding amount. I had also given them explicit permission to communicate with me via email (by default, they can only communicate through the postal service).

This situation suggests two possibilities: 
1- They took four months to notice that I hadn't made a payment, then seized the opportunity to fine me. 
2- They knew I was in default and waited the required three months before imposing a penalty.

I will never know which scenario is true because of how incentives are aligned with tax agents in Spain; either could be possible.