Pretty much same answer as before on other forum - normally it's one per packet. BUT - I've done 3 or 4 AEB-L blades to a packet. I think HCS was only 1 layer deep, but I have put small blades two deep and allowed more time to soak to account for the extra thickness, then plate quench. For sure laying 2 or 3 blades a single layer deep wouldn't be any problem - should be the same as one large blade of same thickness.
When making folders I normally put backspring and blade in same packet for HT then plate quench.
The only way to go more than one blade per packet is to experiment, and work out the ramp and soak times required for the added mass. Then there's the issue with cooling/hardening...... whether that be air or plate...... it'll be a circus trying to get multiple blades out of the envelope and cooled fast enough to achieve full hardening.
My advice..... keep it to a single blade per envelope.... simpler process, with far fewer chances of ending up with a train wreck.
I've done 20 in one envelope...A2 and airhardening them...I practiced hanging them a few times lol...I slid the pack out of the furnace a bit...cut it open...slid it back in and started pulling and hanging the blades...my son was turning the hanging wheel so all I had to do was get them on the hook that was right near the furnace door. they all came out at 60-61 RC...except the one I dropped on the floor. But not a fun process....(I don't want to do it again...lol) they were very clean though...no scale just a smooth gray.
My next batch of blades I'm bolting together and cooling as a block using pressurized air in a fixture. I think this way they will stay straighter. The other way I had about 5 that warped...
I often put two or three in the same foil. Make sure they aren't stacked is all. I have put in multiple envelopes in for heat, pulled one out quenched, pulled the next and quenched and so on. The oven dropped nearly 250F degrees as I did that. I only put in what I can quench quickly at one time.