[Q] Which xt321 SBF is newer?

[kc1]

Hi, just got an xt321 second hand. The current software is:

Android: 2.3.6
Kernel version: 2.6.38.6+
Build Number: 05.28.0B
Flex Version IRD_SEA_Retail_v9_0516_FLEXTNBST
Baseband version: 76XXU-USMEKOLYM-109806-7622
Software version: TNBST_4_05.28.0BRPD

Looking around, I can see SBFs for the UK (here), including:

TNBST_4_0A.21.21RPS_flex_WE_RTGB_v14_0512_NOAPR_sec_20120514, and
TNBST_4_0A.21.0ERPS_flex_WE_RTGB_v13_0323_NOAPR_sec_20120323

...which look like March & May 2012. Is the software I have currently installed the most recent/up to date?

Thanks