In the Levitt paper, 64% is the number of single-domain architecture proteins that are found in at least two of the 3 groups viruses, prokaryotes, and eukaryotes (figure 3). This is my (very close) approximation for the fraction of families in eukaryotes or prokaryotes found in both eukaryotes and prokaryotes, which isn't reported. 84% is computed from that information, plus the caption of figure 3 saying that prokaryotes contain 88% of SDA families. 73% is computed from all of that information.

Most proteins have not been discovered - and there is probably a bias towards discovering the ones that are shared with eucaryotes - which would distort the figures in favour of finding older genes.

There is no bias towards discovering genes shared with eukaryotes in ordinary sequencing. We sequence complete genomes. Almost all of the bacterial genes known come from these whole-genome projects. We've sequenced many more bacteria than eukaryotes. Bacterial genomes don't contain much repetitive intergenic DNA, so you get nice complete genome assemblies.

Life starting 3.7 billion years ago - could be. Google's top ten show claims ranging from 2.7GY to 4.4GY ago. Adding that .7 billion could make the information-growth curve more linear, and remove one exponentiation in my analysis.

Also, it seems rather dubious to measure the rate of information change within evolution as the rate of information change within bacterial genomes. That doesn't consider the information present in the diversity of life.

Let's just say I'm measuring the information in DNA. Information in "the diversity of life" is too vague. I don't want to measure any information that an organism or an ecosystem gains from the environment by expressing those genetic codes.