The top stamp has the matt carmine cross overprint and the bottom stamp has the shiny vermillion overprint. I think the middle has a fake red overprint. The ink is just not the same and seems to be of a lower quality. The resulting overprint seems less well defined.
The fake overprint is more obvious in the middle stamp here. The ink is definitely of a different shade and quality. They do not have the translucency of the carmine overprint nor the brightness of the vermillion overprint. They are both quite well executed and probably hand painted on properly used stamps. They could have passed off as genuine if one does not have a normal stamp to compare.
I have seen much cruder productions where the cross is of a different size and proportion. The other tell tale sign is that a bar CTO stamp was very often used. Genuine Maltese cross overprinted NB stamps were not officially cancelled to order with bars.
The stamps of the 1925 issue with perforation 12 has also been used in forging these stamps.