Experiments have confirmed this effect: New generations of clocks continuously improve the accuracy; eg, Tino et al. 2007.

there were a few theoretical disappointments: Earman 2001 gives a detailed, excellent (technical) discussion of Einstein’s introduction of the cosmological constant and its early history. A clear exposition is also North 1965 (see also Norton 2000).

Willem de Sitter found a solution: de Sitter 1917.

“If there is no quasi-static world”: Einstein’s letter to Weyl on May 23, 1923.

In a paper published in 1931: Einstein 1931.