New, unused Pektron fob comes with 22 number barcode. This barcode represents window within which Pektron alarm system will recognise the fob and accept it when barcode is entered into Pektron system.
If fob is pressed several times it will roll its code, but Pektron system can still recognise it when barcode is entered. If fob is pressed too many times barcode cannot help anymore as code rolled outside barcode window. How many times fob can be pressed and to still be within window, knows Technozen. But if fob is pressed only once, it is still within window.
This is the reason why used Pektron fobs cannot be reused even if you have original barcode.
Only way to reuse old fobs is to either have Pektron alarm system ecu with the fobs or to clone Pektron alarm system ecu to new Pektron ecu which Technozen can do.