What was the general policy about working with law enforcement to prosecute such attempts, to the extent they were traceable?
Both backdoor requests I became privy to while there (2.5 years, circa 2011-2014) came from a certain US TLA, were law enforcement would have been an awkward step, though it seems reasonable to me that there were more requests, including from other organizations, but I was never made aware of those.
There were some foreign spies caught in MSRC in the same timeframe. More of an extradite than a prosecute type situation, though.
If Jonny Law goes after you for that the company will cover you, because while they might be OK to take the company decision to cooperate, they can absolutely not have random rogue employees doing that. Since the threat of law is what may make those employees comply, they need to make is as little threatening as possible, thus full legal support.
The reason to omit all others is that at this point you don't know several things: is there an already existing investigation that you are now part of? Is your boss or anyone you work with implicated or suspected in it? And so on.
The only other thing you may wish to consider is if you want to discuss it with your personal attorney first. If you think you may have some legal exposure (it is very difficult to know, as a lay person, wether you do or not) you may want expert advice before informing the company. In any case proceed quickly, do not delay in informing the company unless so advised by your attorney.