I have posted several claims by former NYCACC employees that Ed Boks, at some point, made a policy decision to exclude owner requested euthanasias from euthanasia in general, which might explain 4% of the improvement in NYC's euth numbers.
A current allegation is that a lot of the "impounded" animals in the NYC shelters are actually still in the care of people who found the animals, and that the total number of currently impounded animals is: 181 cats, 140 dogs and 21 other animals, which is 342 animals on hand, including those at finders' homes.
On the other hand, LA currently (according to info on animals per shelter on the LAAS website) has curreently impounded: 1,100 dogs, 950 cats and 950 other animals. Therefore, according to calculations based on these observations/allegations, LAAS has warehoused 9 X the number as NYC.
This is relevant to Philly also, who currently has 120 dogs and 180 cats on hand (according to my sources. This may not be true; this may be the number of cat cages and dog kennels and the number of animals on hand may be triple that). I don't know how many Philly has in the "Other animal" category, if even they have any. Again, LAAS warehouses 10X as many as Philly.
The huge capability of LAAS to warehouse animals accounts for a lot of the decrease in killing. Until very recently, there has been no increases in adoptions or fosters. Even these would not explain the decreased killing. Not accepting neonatals would explain a lot, but warehousing them explains more.
The huge warehouse space allows LAAS to keep euth down for a much longer period of time than either Philly or NYC.