At this moment I'm working with the NFC module PN532, I have 2 modules of this reference. They are apparently equal, but they don't work equals. With the module #1 I can read the UID of differents Tags (Credit card, buy pay car, bank card and Mifare classic), with the module #2 I can read the UID only in the Mifare Classic card.
One important thing about this modules is that with the module #1 I can read the UID at 5 cm, with the module #2 I can read the UID at 2.5 cm, so I think that maybe the module #1 have more antenna Gain and can read the other tags.
Also I've saw the reference in the main chip in each module and they are different.
Module #1 chip reference: 5321 06 CXX963 02 TS09501
Module #2 chip reference: 5321 06 CWW607 08 TSD9181
Both modules have the same distribution and pcb, all the tracks are equal and the position of the components is equal.
I think that there are 2 possibilities:
the first one -> some capacitors or inductors have a different value and the antenna gain is higher, then the module #1 can read the more secure cards (Credit card, buy pay car, bank card).
the second one -> the chip reference is very important and the reference 5321 06 CWW607 08 TSD9181 can't read this kind of tags.