I doubt you found overweight half reales - more than likely they were underweight one reales. I have a one reale from Lima that weighs 2.1 grams. The Spaniards didn't mint overweight coins - they were always trimmed to exact or slightly under correct weight.
(I will be nice)
more likely underweight 1's...ah nope, I'm positive 1/2 reales. Planchets were huge very much like a 1 but struck with 1/2 real die.
Believe this ! There are Authentic Genuine Cobs time period cobs that were both struck 1. Overweight and 2. Underweight but yes I will agree (not the Standard) but just like Mints of today, errors did get through the system.
As far as the Spaniards trimming to exact weights or under cutting weights? The Spaniards? not sure they did any of the real work involved with either the actual Striking, Weighing and trimming of the cobs...I'm leaning towards more like the native Slaves who were "employed" by such Spaniards. The Spaniards were too lazy to actually "work" but they did manage the mints, did the designs of the dies, maybe assayed the silver, and approved some of the quality control, as they were responsible for that...but a Spaniard doing the actual work

, LMAO. Even today Spain doesn't work for the minted coins they lost, they wait till someone else does the work and then they step in and take all the credit.
Cheers,
True - As the general rule of thumb...be suspect of overweight/underweight cobs and 2nd
Never believe a Fishermans tale (Jedi mind trick)
Trez