This definition appears somewhat frequently
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[Note for the purists. We're not counting the provisional temperature scales, although we know of two of them, the Provisional IPTS of 1970 and the new, Provisional Low Temperature Scale of 2000 (PLTS-2000). The latter is for temperatures below 0. 65 K, the low limit of ITS-90.
CCT has also adopted a mise en pratique (practical instructions) in 2011.  The lowest temperature covered by ITS-90 is 0. 65 K. In 2000, the temperature scale was extended further, to 0. 9 mK, by the adoption of a supplemental scale, known as the Provisional Low Temperature Scale.