Maybe I'm missing something or AA is getting away with murder also...however, FWIW
At AA, 'on duty' and 'on call' are not the same thing with a couple of exceptions.
The "six-day countdown toward a mandatory day off" starts with the first day you actually fly. If you sit at home on call, this does not count toward the six-day requirement.
Now our reserve system is different from yours, but say for instance, I have a line month in September and I am on reserve in October. I fly the last day of September and I am scheduled to be available for reserve assignment the first six days in October. Even if I am not used for 5 days, I still get that sixth day off because the block of "on call days" (what we call ready reserve) was preceded immediately by a day of flying.
If I don't fly the last day of September and I sit on ready reserve unused the first five days of October, they can give me a trip for the 6th and 7th (even though that was scheduled as a day off) as long as I am back at base by 12 noon on the 7th. My block of days off (let's say 3) then start 15 minutes after the end of the trip and "rolls" to that time on the 10th (which was supposed to be my next ready reserve day starting at midnight on the 9th). Trip ends at 10:45am on the 7th. Next "available day" begins at 11:00am on the 10th. They can, however, assign me a trip where I have to sign-in at 11:01am on the 10th.
R=Ready Reserve (on call)
X= Day off
1 2 3 4 5 6 7 8 9 10 11 12 13 14
R R R R R R X X X R R R R R
One of the things in our contract that "helps" the company is that we have 12 mandatory days off per reserve month; however, one of those days is Moveable. With 24 hours notice the company can move that day off anywhere on your schedule whether you agree or not. So, if I fly on 30Sep they will probably move my day off to one of those 1st 5 days so that I don't show a 7D (7-day legality) on my schedule.
At AA they are getting pretty good at avoiding giving f/as a 7-day legality day off. Mostly they create the reserve lines with fewer than 6 days straight "on call" so it would be impossible to occur. Something like 5 days on, 3 days off, 4 days on, 4 days, off, 5 days on, 3 days off, 4 days on, and off last 2 days of the month.
One of the things that I have noticed on reserve is that even schedulers sometimes confuse 30-in-7 (which is a contractual issue) restrictions and 7-day legality (which is an FAA issue).
BTW, as I understand it, the way AA does it has been fully blessed by the FAA in writing.