yes it is possible to transmitee 512 channels (even more than 512)
in the case for ht12d and ht12e
you have you have 4 bits to transmmite
so you can make your combination like
D0 D1 D2 D3 work
0 0 0 0 do task 1
0 0 0 1 do task 2
similarlly u have 16 combination from 4bit at a single address
and we have 8 address lines so total 255 addresses
so we can transmits 16 * 255 signals by using ht12d and 12e itself *(but for that you need to go with microcontroller)
calculate yourself for 640 and 648…..