How is it not possible? It's just additional votes, there isn't anything actually stopping counting by hand, is there? How was it counted historically without voting machines?

It takes a lot of people (redundancy and to keep shift hours low to increase count accuracy) to accurately count by hand. https://verifiedvoting.org/election-system/hand-counted-pape...

That makes it difficult, but the original comment said it wasn't 'possible'. I'm failing to see the impossibility still.