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.