After much back and forth with NXP over the issues with the xSIID and accessing all 2k, it appears that android and iOS simply choke on trying to read ndef data that skips over a reserved section… and after reviewing the NFC Type 2 forum specification, there clearly is no provision for handling memory topography like that. The Memory TLV definition simply handles a single reserved section but there is no provision for reading memory beyond it, so basically the phones and reader chips in the phones can easily access that extended memory sector on 2k NTAG I2C chips, and you could also easily write your own mobile applications to do so, in the end the NFC library functions in both phone OSes which read and parse the data simply trip over it and land on their faces.
As such, these cards currently have 2k chips but they have been set up with a CC (capability container) that only addresses the first 1k for NDEF data. New cards, if they are made, will have 1k chips. The same is likely to be true for the next batch of xSIID as well.