I have taken a day to look at the papers/watermarks of the'cents' values-all small format excluding the most common ones (5c, 10c, 15c, and 20c). This table shows the ones I find.
1ct: 1 c typographed
2p5c: 2 1/2c
12cBR: 12c Brown
12cR: 12c Red
Y: Yes, I find it
O: Only found overprinted 'Servicio Oficial'
SD: side-to-side, that is, horizontal
UD: up-down, that is, vertical
The 1L5 is the 'Zarate' paper which can sometimes seem not to have a watermark and is very thin.