I recommend bunching the papers into the following five groups:
1. All of the Wavy Rays stamps before 1945 (1E3). These are all type A.
2. Unwatermarked (NGR and NOP, latter I only find as Servicio Oficial). These are all type A.
3. Clay papers (four, two before 1945, and two after). These are all type A.
4. The straight rays types A and B, especially the very rare reddish brown printing.
5. The late Wavy Rays values (1L1 and 1L5Z-Zarate). The 1L1 is type B, and the Zarate values are type A.
Using the papers as a guide is a good starting point because the color of the paper affects the color of the stamp as we see it. Several examples are worth mentioning:
1. The NGR is a low quality paper that often discolors with age.
2. The straight rays paper, the 2C, is bright white.
3. The Zarate papers are grayish.
Once we have grouped the stamps into these five categories, categorizing shades becomes a more controllable process.