This is what happens with the Earth's excess angular velocity (momentum) over time


Note the strong hiccup ~1983 where it appeared the earth's rotation slowed down temporarily.

That coincides with the point that the SOI model also loses coherence with the underling data.

This is a prior analysis:'s%20Rotation.pdf
Chao, Benjamin Fong, and Isao Naito. "Wavelet analysis provides a new tool for studying Earth's rotation." Eos, Transactions American Geophysical Union 76.16 (1995): 161-165.


Like they say, what is confusing is the QBO has the opposite polarity when comparing the two events.