dating system in Walls of Eryx

[thinkbolt]

At the beginning of paragraph 2, a Venusian day/date system is established.

"I reached the main landing on Venus March 18, terrestrial time; VI, 9 of the planet’s calendar."

I assume this is pronounced "vee-eye?" As in "Venus something?"
Does anybody have an indication of what the "I" stands for? The name of a Venusian month? Or something else?

[Genus Unknown]

Could be Roman numeral 6. Sixth month, ninth day maybe?

[thinkbolt]

I hope not, Genus.

[Genus Unknown]

Why not?

[thinkbolt]

'Cause that would be really uncreative, and I expect more interesting stuff from Lovecraft.

Has anybody seen any author's notes about this story?

[Genus Unknown]

'Cause that would be really uncreative, and I expect more interesting stuff from Lovecraft.

Yeah, but "Eryx" is a collaboration, which usually means he's phoning it in.

It's also possible that he didn't invent anything at all, and was just using an actual established system, like something used by astronomers. I can't back that up though, because a  Google search for "Venus dating system" just pulls up a bunch of stuff about Mayans, who apparently used Venus to calculate dates in some manner.

[old book]

I'm almost positive it's what Genus said, the Roman numeral VI for 6 for the number of the Venusian month followed by the day, 9. It used to be more common to use Roman numerals for the months, fairly standard procedure. I doubt Lovecraft or the other author delved too deeply into the rotational periods of Venus. March 18 rings some bell though, wasn't that the date Mt. St. Helens exploded in 1980?