I think the operative element here is the amount of B12.

Clearly a shot a day for a month is a lot more B12 than one 1,000 mcg B12 lozenge a day for a month.

It is my feeling that people who have replenished their B12 supplies using lozenges, and who have had episodes when things stopped improving and instead got worse, were feeling the effects of some temporary additional drain on their B12, like a particular stress, and that had they realized the connection, they could have upped the amount they were taking with beneficial results.