IMO, the two expansion rates -- one from the CMBR representing the expansion rate 13.8 Gyrs. ago; one for the rate today -- simply tell us that the expansion rate of space is not fixed for all time. Given the discovery of DE, the arguments from scientists that DE's influence over spacetime is growing would require that these rates differ.
How can we claim the universe is, and has been, accelerating but require it to always have one speed? What good is acceleration if nothing can go faster? [I once had a car like that.
] I've yet to see an explanation for this simple question.
Also, the reason the Hubble Constant is now called the Hubble-Lemaitre Constant is because astronomers like to give credit where credit is due, but because of the remarkable clout and contributions from Hubble, the other two key players got set aside, apparently.
For those interested in the BBT story....
BBT Chronology:
1912 -- Henrietta Swan Leavitt gives us the Cepheid variable law that allowed for galaxy distance determinations, necessary to find their expansion rates.
1912 -- September 17 Vesto Slipher found, with great effort, the first redshift data for galaxies (extragalactic nebulae).
1914 -- In a meeting of the American Astronomical Society, Slipher presented results for a total of 15 distant nebulae (later called galaxies). He was so convincing that his results were received by the audience (chronicles say) with a very long, standing ovation. Apparently, this is unusual.
George's Lemaitre was at that meeting.
1915-1916 GR (General Relativity) introduced by Einstein.
1917 – Einstein used GR to build a cosmology model.
1922 Alexander Friedmann found a math solution of Einstein’s equations suggesting the universe could be expanding or contracting. Einstein rejects this idea since the status quo was for a static universe.
DeSitter, and others, offered models that allowed for redshift in a static universe. DeSitter's model, for example, worked fine as long as his universe included no mass.
1927 -- Independent of Friedmann, Lemaitre, using GR, published (in French) his theory introducing not only the math for an expanding universe, but also evidence for this expansion (i.e. physics). His paper is entitled ‘Un Univers homogene de masse constante et de rayon croissant rendant compte de la vitesse radiale des n´ebuleuses extra-galactiques’. There's no evidence anybody every read this Belgium work.
In this paper, Lemaitre introduced the world's first estimate for an expansion rate for the universe. He used the redshift data from Slipher and the galaxy distances from Hubble. Combining these gives an approximate expansion rate.
In 1929, I think, he listened to Eddington claim there was no explanation for the redshifts. He translated his original paper and soon the prominent scientists had their explanation. But Hubble had greatly improved the data, so Lemaitre left out his cruder estimate for the expansion rate, opening the door further for Hubble to get credit, accidentally.
Einstein stated that his math was fine but his physics was "abominable". [Einstein was stuck on the enduring Static model, but others soon un-glued him once Lemaitre gave an English translation to Eddington, who gave it to DeSitter. They quickly recognized its importance, as did Einstein.
Hubble, with the Hooker telescope and Humason, greatly improved the accuracy of both the distances to galaxies as well as, their redshift. Surprisingly, Hubble never stated that he held that the universe is actually expanding. His graphs imply otherwise, admittedly, but I would bet an ice cream sundae that no one can show where he published anything explicitly stating the universe is expanding, though I could be wrong, as well as several science writers, btw. Hubble stated that he was an astronomer, not a theorist. [He was also friends with deSitter, if that's a factor.]