I can't address some of your other questions about a same day change but in regards to availability;
AC 016 is showing a few open seats in economy, and is definitely not oversold. I would assume that revenue management would open up R space in a few days if both J and Y remain >5
[KVS Availability Tool 7.0.2/Diamond - Sabre: Availability/FS/US]
Code:
HKG Hong Kong Intl HK [VHHH]
YYZ Toronto Pearson Intl ON CA [CYYZ]
SAT 04 Aug 2012
Carrier Flight From Depart To Arrive A/C St Availability
--------- ------ ---- -------- ---- -------- --- -- -----------------------------------------------------------------
AC 16 HKG 15:10 YYZ 18:05 77L R0 Y9 B8 M1 U0 H0 Q0 V0 W0 S0 T0 L0 K0 N0 G0 P0 E0 A0 J8 C5 D3 Z0