By default, an RFID reader reads block zero’s content first. Can I change that?
Memory block zero is the first user memory block on a passive UHF transponder. The device will typically read the serial number in the tag (its Electronic Product Code or some other unique number), then read the first memory block, then read the second and so on. It would make the most sense to store your data in memory block zero and have that read first. If you wanted, for some reason, to store data in another block and read that first, you would need to check with the manufacturer of the specific reader you are using to find out if that is possible.
—Mark Roberti, Founder and Editor, RFID Journal