  Nuclear Magnetic Resonance (NMR) is a powerful local quantum probe of the
electronic structure of materials, but in the absence of reliable theory the
interpretation of the NMR data can be challenging. This is true in particular
for the cuprate high-temperature superconductors. Over the years, a large base
of NMR data became available, which makes a review of the early interpretation
possible. Recently, it was shown that all planar $^{17}$O NMR shift and
relaxation data available in the literature point to a temperature independent
but doping dependent pseudogap, very similar to what was proposed from the
electronic entropy. Here we analyze the anisotropy of the shift and relaxation
of planar O to establish whether a single electronic spin component is
applicable, since the planar Cu shift anisotropy clearly fails such a
description. We find that the orbital shift terms deduced from the data are in
agreement with first principle calculations, and the shift data show a
temperature independent anisotropy also in agreement with hyperfine
coefficients predicted by first principles, which also account for the
relaxation anisotropy. Furthermore, we show that the original $^{89}$Y shift
and relaxation data are in agreement with the proposed temperature independent
pseudogap. This pseudogap depends on doping, but also on the family of
materials, and the density of states outside or in the absence of the gap is
universal for the cuprates; this suggests that the entropy should be similar
for all cuprates, as well. Further consequences will be discussed.
