I've been successful a couple of times using EF while cherry-picking with a Flex Pass (this was many years ago). This was a couple days out. Both times received an op-up (both transcon XM widebody). (forgot to say that these flights did ask for volunteers)
But for the most part, it's tough IMHO. I usually ask employee friends (or others who have access) for the actual negative Y load.

Using public tools can be hard. Sometimes a flight is J0 O0 Y0 and it's overbooked by 30. Sometimes it's not overbooked at all.

But even with internal access, I've had times where SFO-YYZ was negative 30, but due to various issues, including pax not having ETAs, we left with 20 empty seats.

I wanted 117 because it was the latest I could leave YYZ today, flying J to SFO. It was J7 or something when I booked it. It would not have been the flight I picked if VDB were my primary concern.

GAs were offering $1400 each for 2 pax to VDB from tonight to a tomorrow morning YYJ-YVR flight. Last flight of the night (8168 @ 1850) overbooked.

Mini melt down out West with QK today it seems. Numerous weather & “Covid crew constraint” delays.

There were fast takers, right?

Was one of three to pick up $2400 on YVR-SEA this morning. Bumped just over nine hours to a flight this eveing. Gate agent didn't actually process the rebooking or the compensation voucher, which led to two and a half hours of waiting on line / for manager overrides to get the compensation sorted, but worth the wait.

AC222 YVR-YYC. Was on my way to the gate when I heard them saying over PA oversold, looking for volunteers $1400 plus accommodations, next flight out in the morning. People rushed up to take it.

I’m Visiting family and have to head back tomorrow so I Couldn’t have taken it but what a deal!

Flight was completely packed and my suit garment bag got squashed by all the extra luggage that needed to be stored lol.

Was on a TPAC from YVR yesterday and the SD mentioned to someone that they oversold J class and had to bump some folks into Y. Did not hear what the comp was going for but that would be a sucky 10 hour flight for some.

How did they actually oversell J? I thought that this was something they studiously avoided.

Or was this something else?

I agree it's super odd but the SD quite definitely said they had overbooked J - no change in equipment, no other cancellations, it was YVR-NRT.

AC3 YVR-NRT is normally scheduled for a 789, but yesterday's flight appears to have operated on a 788.

If so, then J wasn't "oversold", the equipment swap to a smaller version of the same aircraft will have reduced the number of physical J seats from 30 to 20.

...but the SD definitely Works At The Airport, so it must not have been a 788.

AC3 was a 788 the previous Thursday too.
Could be a day of the week thing or a last minute a/c swap.

Scheduled for a 788 this coming Thursday, but a 789 the three Thursdays after that.

One imagines that if it were a regularly-scheduled thing, they'd have sold the appropriate number of seats in J.

It could also have been a last minute pilot deadhead or something else that forces the cabin into an oversale.

AC does not, as a matter of policy, sell more seats in J than are available.

Deadheading a pilot out to NRT (and in this case multiple pilots, since OP mentioned "some folks" got bumped) would be unlikely to come up unless a whole flight crew had gotten COVID or something.

Agreed, but "some folks" also assumes the SD actually knows what happened.

I had an SFO-YYZ in actual proper paid J, as SE, and the SD was told not to give me a meal. The SD mentioned something like "we don't have enough meals, and you're an upgrade".

But I wasn't an upgrade. So someone else overhearing the conversation (which appears to be what happened in this case) would have inferred an inaccurate depiction of the events, because there was a very short game of broken telephone between the GA and SD, and then the SD filled in the gaps with assumptions.