You might have a problem on your hands, they are now entering all new data in a central computer, and the next time that you apply for a visa it will be registered.
When you do not turn the visa in and you request a new one do not be surprised if you are turned down, they are geting stricter.
Mexico also has an ilegal inmigration problem on the Southern border with all the Salvadorans and Honduran migrants that do not make it to the US border and stay in Mexico, so threy are going to get tougher on all borders.
Do not be complacent, you have been lucky so far, next time you might get a rude surprice.
navegator