It's really just counting more as numbers. The first cache would've been GCA, then GCB, etc. Groundspeak has letters used as numbers, as well as numbers themselves. So really its just cache placement numbers. They go it thei order: a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, z, 1, 2, 3, 4, 5, 6, 7, 8, 9, but zero may be included, not sure. Older ones just use regular numbers.