I made a serious oops last time I did my Greatest Lefty of All-Time argument; I included Translated Career ERA's from the Davenport Translated Cards, but I did not include ERA+. So here are the same top candidates again, with career ERA+ included as well:

Here are some important career numbers so far (ERA is from the Davenport Translated Cards, so ERA is translated for all-time):

Randy Johnson: 129.0 WARP3, 45.3 Peak WARP, 87.15 JAWS, 1308 PRAR, 4195 K, 1308 BB, 3.01 ERA, 144 ERA+

Steve Carlton: 130.7 WARP3, 40.4 Peak WARP, 85.55 JAWS, 1403 PRAR, 4,136 K, 1833 BB, 3.45 ERA, 115 ERA+

Sandy Koufax: 68.8 WARP3, 47.8 Peak WARP, 58.3 JAWS, 785 PRAR, 2396 K, 817 BB, 2.70 ERA, 131 ERA+

Warren Spahn: 161.3 WARP3, 50.4 Peak WARP, 105.85 JAWS, 1651 PRAR, 2583 K, 1434 BB, 3.18 ERA, 118 ERA+

Lefty Grove: 127 WARP3, 49.1 Peak WARP, 88.05 JAWS, 1297 PRAR, 2266 K, 1187 BB, 2.99 ERA, 148 ERA+

Tom Glavine: 122.0 WARP3, 42.1 Peak WARP, 82.05 JAWS, 1221 PRAR, 2262 K, 1292 BB, 3.51 ERA, 121 ERA+

Carl Hubbell: 100.8 WARP3, 54.6 Peak WARP, 77.7 JAWS, 1027 PRAR, 1677 K, 725 BB, 3.37 ERA, 130 ERA+

Hal Newhouse: 102.4 WARP3, 60.6 Peak WARP, 81.5 JAWS, 1005 PRAR, 1796 K, 1249 BB, 3.08 ERA, 130 ERA+

The bolded number is the leader in each category; if we go simply by counting categories, Warren Spahn is the greatest southpaw of all-time. Johnson is the most obviously dominant pitcher on the list, with the most K, but the greatest performances seem to come from Hal Newhouse's brilliant 5-year peak (netting that 60.6 Peak WARP) and Spahn's career length, plus his 11 years in a row hovering around 8-11 WARP3 per season merits massive kudos. Of course, Lefty Grove was the best pitcher on the planet for over a decade, so he is also included. Not to mention his ERA+ of 148 is the greatest all-time for lefties, and second best all-time behind Pedro Martinez's incredibly insane ERA+ of 167.

So basically this is what we are at: If longevity is your thing, Spahn is your man. If you want a slightly shorter stretch of career with more dominance, Lefty Grove is the southpaw for you.

If Johnson is able to be dominant for another 3-4 seasons, we might see him topple Spahn and Grove. Let's take just the two of them next to each other, and throw a few more numbers Johnson's way to see if he can pass them in career value, and therefore as the greatest lefty of all-time.

Johnson has been given 7.5 WARP3 for the next 3 seasons, plus 100 PRAR for the next 3 years, with additional K's and BB's thrown into the mix as well.

Randy Johnson: 151.5 WARP3, 45.3 Peak WARP, 98.4 JAWS, 1608 PRAR, 4870 K, 1503 BB

Warren Spahn: 161.3 WARP3, 50.4 Peak WARP, 105.85 JAWS, 1651 PRAR, 2583 K, 1434 BB

Lefty Grove: 127 WARP3, 49.1 Peak WARP, 88.05 JAWS, 1297 PRAR, 2266 K, 1187 BB, 2.99 ERA, 148 ERA+

With these additions to Johnson, he is close enough in WARP, JAWS, and PRAR that we may able to state a case for him as the greatest left-handed of all time. Surely, given a fourth season of 7.5 (which would be fair, since he could post an 10 or 11 and a 5.5 or so in the next 4 years) as well as another 100 PRAR, we come to this:

Randy Johnson: 159.0 WARP3, 45.3 Peak WARP, 102.15 JAWS, 1708 PRAR, 5095 K, 1499 BB

Warren Spahn: 161.3 WARP3, 50.4 Peak WARP, 105.85 JAWS, 1651 PRAR, 2583 K, 1434 BB

Lefty Grove: 127 WARP3, 49.1 Peak WARP, 88.05 JAWS, 1297 PRAR, 2266 K, 1187 BB, 2.99 ERA, 148 ERA+

That last season of added on numbers may very well be what Johnson needs to surpass Warren Spahn and Lefty Grove as the greatest southpaw in history. His WARP3 and JAWS scores are close enough, especially considering the massive gap in strikeouts and the 57 additional PRAR over Spahn. Will Johnson be able to get the additional 30 WARP and 400 PRAR in the next 4 years? Maybe not (he will be 45 by then after all) but that is what it may take to take the imaginary crown away from one of these pitchers as baseball's premier lefthander. It is not that out of the picture; Johnson has come on strong the older he has gotten, and Spahn retired when he was 44. He was not effective his last 3 seasons, but maybe conditioning, better health, and the fact that Johnson's dominance has not withered may help him string those extra years together.

If not, then we have two answers for the greatest lefty of all-time, depending on your preference: Spahn has more WARP and a better JAWS due to more seasons, while Grove has the greatest ERA+ of all-time among lefthanders. Maybe Johnson will continue to blow away the competition with that fastball/slider combo (and his 144 ERA+, close enough to Grove's to give it to him considering the 2,000+ K gap) and the issue will be settled once and for all.