Staff are trained to only permit those at or over the height restriction, if it gets out that they let someone under the height limit, they will get disciplined and instantly taken off of the ride, and depending on how serious the offense is, potentially even straight-up sacked.
A lot of coasters with 1.4m height limits are not actually the hard height restrictions, and are often a few centimetres over. Most of the 140cm height limits at are actually 137cm according to manufacturer brochures, this is why similar ride models sometimes have lower height limits, however because of operational/insurance procedures they are 1.4m most of the time, so on the off-chance someone is a centimetre or so off the mark, nothing will happen.
Ice Breaker at SeaWorld Orlando is also a prime example of a manufacturer getting it wrong as well, it's always better to be safe than sorry.