In all my research, I have found most transmission services were done after 100,000 miles. Yes, there may be a small percentage that did it religiously at 60,000 miles but I can only guess less than 1 or 2 percent of the owners followed that service interval.
I guess maybe the best route is maybe doing the filter and fluid change as this is still leaving 40% of the original fluid and see if it causes any problems for a week or 2. One look in the pan magnets should give some kind of indication that there was a problem that would have been inevitable.
I have avoided the transmission fluid changes exactly because of the issues you pointed out but I feel the pampered mileage along with zero transmission issues allows me the confidence this will only be a benefit.
Hopefully RRPhil posts some of his knowledge for all of us.