Adtran 908e 2nd gen - PRI to Mitel system

[AH64Armament]

We have a site that has a carrier-provided TA908e gen 2 that was installed in October 2022 and is running R11 firmware.
This carrier has relinquished support of this Adtran to the customer and subsequently my company, stating that they will continue to provide SIP service, but they don't have any knowledge of that Adtran and we now need to maintain it.
They provided remote access to us and I've logged into it to gather config and other info.
We have since purchased a spare 908e that is running R10 firmware.
I'm curious as to why they wouldn't have installed a newer firmware to the system as at the time of install, the available firmware was R14.1.1.
Adtran's firmware download section doesn't even show the version that we have on site or our spare.
As this site is 2+ hours away, I don't dare install the latest R14.2 or any other version without first asking the questions to see if it should be done.
Meanwhile, I'd like to get R11.5.1.E so I can at least make sure our spare has the same version and I'm able to load their config to it.
I haven't worked on any Adtran products in nearly 10 years and I feel like a fish out of water... the last ones I worked on were Netvanta switches and routers.

Any help would be very helpful.

 

[jpruder]

Looked and my unit is at 11.4, it's a gen3 but would think having the current firmware would be best as it may have been bug fixes forcing it to this level. Looked online and no longer have Adtran access as of my layoff. Seems you need some special i.e. corporate email to get access. Makes it hard for me and all the products of theirs I have to provide any support IMHO.