Hey there!

I own 3 Deco X60. All bought in a 3-pack on Amazon. 
One is HW 4.2 the other two are HW 3.2. Don't ask me why not all 3 have the same HW version... 
 

Only firmware 1.2.5 (for HW 3.2) and 1.2.9 (for HW 4.2) are available here https://www.tp-link.com/de/support/download/deco-x60/.

The latest one before 1.6.0 was 1.3.0 which was months ago. Perhaps you can update your site with 1.3.0 and 1.6.0.

 
PS: Oh and by the way as a technican from TP once told me the firmware for HW 4.2 is also compatible with HW 3.2. I found firmware 1.6.0 for HW 4.2 on the Nordic X60 site here https://www.tp-link.com/nordic/support/download/deco-x60/#Firmware - and flashed it via browser. All working, even the HW 3.2 Decos have been updated.