First of all, Merry Christmas everyone!
Ok, so last night I couldn't sleep and was toying around with the bedrock glitch. Turns out it's definitely a thing. I managed to collect 8-9 more bedrock during the Day 42 horde. I haven't figured out a consistent way of doing it, but here's what I know so far.
The zombie has to be standing on bedrock. When you kill a zombie, you need to use a spiked club and hit their "corpse" until it turns into "zombie remains." For some reason, the transition between corpse and remains gives you 1 bedrock. This isnt consistent however, and seems to be random. One thing that does seem to increase your chances is if you can smack the corpse while it is still collapsing to the ground, turning it into remains mid animation.
I'm sure there's some consistent and easier way to exploit all of this. I'll keep trying and update accordingly. The exciting potential of all this is that you can build an invincible base out of bedrock, rather than having to resort to cheesy tactics to deal with hordes.