Guessing, not informing
Guys, before anybody takes my messages as "info", I have to tell you: DON'T DO IT. I'm just guessing like many others. I don't think there's any inter-agency agreement, it's just that USCIS is trying to keep their backlog as low as possible and avoid any lawsuits coming from people who's PD is old, but get their LC cleared later. If they let PERM guys get their GC before these backlogged, there will be surely some lawsuits and congressmen inquiries. "Enforcing the FIFO" is just the result of their self-protection.
For those of us, who have old PDs, but still in SWA stage, it's good news, for other backlogged applicants with later PDs (like me) it's not so good, but at least it shows some order, and for those in PERM, it's very bad.
I don't think USCIS cares how many PERM applicants have filed I-485. What matters is that probably non of them has got the GC yet, so their cases can be put on the side for a while. They'll probably get EADs, but that's only temporary, so it's not a problem for the agency. Unfortunately, we won't be able to get one for a while...
There's only one thing we can do: DO NOT GIVE UP!