The FCC's still talk to each other (sharing IRU data).
There are some Service Bulletins regarding A/P engagement and the availability of "inner loop" data. e.g. pre-SB 22-xxxx, in the air, A/P engagement requres at least two inner loop sensors being valid (i.e. any two IRS's). Post-SB 22-xxxx, in air, single channel engagement is allowed only if the local sensor source is valid (i.e. local IRU data... e.g. Left A/P requires Left IRU)
Some SB's are not mandatory, but, even so, I'm wondering if the term "engagement" is different to "being engaged and remaining engaged".