I usually travel very, very light and this is rarely an issue for me but from experience my feeling is that AY is very generous with actual J carry-on rules/limits. For example today is one of these rare cases when I plan to take 2 semi-size rollaways as hand luggage on AY's long haul flight and expect no problems whatsoever.

For Y these rules are needed more and I'd wish AY, and most other carriers, would follow them more closely at check-in = quicker boarding process and more flights departing on time.