Actually no, the writer did his/her homework.Lunagel wrote:I'm more inclined to believe the writer didn't pay attention to the first two seasons >.>
While it is not stated in the first or second season (as far as I can tell), paying one day of life to Zaruba in exchange for his service is actually part of the lore and can be found in supplement Garo guidebooks. I remember reading about this in chinese forums few years back and did some quick searches. You can actually found japanese forums/blogs talking about this setting back in year 2011.