Thank you sleepwizard and HiFi oasis for your input.
@sleepwizard - yes I recall seeing that comment mentioned in the Fiio firmware "how to update firmware" guide however it was worded in such a vague way - I wondered if it could be the case that they are warning that if you install the "non bluetooth" firmware over a "bluetooth" unit that you would indeed lose some functionality - specifically the bluetooth feature itself. Admittedly I am considering this entirely based upon interpretation of the comment.
@HiFi Oasis - no I am not experiencing any issues -- YET ... however again my reason for posting is to confirm whether or not there really are 2 versions of the product in terms of the hardware. There are a number of reasons I have considered that it may be the case that what is deemed a "non bluetooth" DM13 may actually be hardware equipped to support bluetooth limited only by the firmware not exposing that service. As I mentioned in my previous post - the documentation specifically calls out compliance with FCC bluetooth requirements - whilst the unit itself (with Firmware v11) does not offer bluetooth as on option ... hence my thinking - how about I try the v25 firmware and see what happens. Furthermore the documentation states "product contained may be upgraded and therefore may not match packaging".
Thank you again for contributing to this topic and yes I do hope
@FiiO Willson can provide some confirmation / clarity on this front.