I've said this 100 times before, but in the 21st century, with even the most rudimentary database technology, this should largely be impossible. Every team line (or even just squad) is typed into an online central system, and it doesn't allow you to submit if it includes an ineligible player. All players registered in the system, with dates signed etc and all cautions recorded post match. It's absolutely ridiculous that we've spent millions on some ridiculous system that measures offside to 1/1000mm, but we are still allowing games to be lost on an administrative error. Frustratingly, we hear this almost every year, yet nobody ever focuses on the solution to this, it's always about blaming the club (usually some part time administrator) as opposed to the system.