All Micro-Groove Model 444 barrels were 1:38" twist, and all 'Ballard-rifled' Model 444 barrels are 1:20" twist. That is correct.
As for barrel lengths...
22" has been the standard barrel length for Marlin Model 444s since 1972.
1964-1971 rifles had 23.5" barrels (MG 1:38").
The few 1963 rifles that left the factory (mostly test rifles that then got sold), and a handful of early 1964 rifles, used rechambered .44 Magnum barrels, and were marked "336-444 Magnum" with several barrel lengths, from 18" to 24". They're uncommon, non-standard, and I don't include them in typical discussions - other than to mention that they're out there. There were all MG 1:38" barrels.
Some later special models, such as the Centennial, were offered with 23.5" barrels (MG 1:38"). There were also the XLRs which had 23.5" barrels. The only outlying oddity was the 18" ported barrel on the 444P ("Outfitter" ... sometimes found
without the porting). Both the XLRs and 444Ps were only offered after 1998, so they're all 'Ballard-rifled' (1:20").
Aside from special models, 22" was the standard from 1972 until 2012.
The 'Ballard' barrels (1:20") were introduced - across most of the 336 family - in 1998, in order to quell customer complaints about cast bullets performing very poorly in .35 Remingon, .444 Marlin, and .45-70.
As for how that all applies to the common models (aside from replacement barrels)...
All original Model 444 barrels were 23.5" MG. (1964-1971)
All 444S barrels were 22" MG. (1972-1983)
--Cross-bolt safety added for 1984, and an additional 'S' added to the model name.--
All pre-1998 Model 444SS barrels were 22" MG. (1984-1997)
Almost all post-1997 Model 444SS barrels were 22" 'Ballard'.(1998-2011 -- A few 22" MG barrels were used in 1998.)
All 444 XLR barrels were 23.5" 'Ballard'.
All 444P barrels were 18" 'Ballard'.
The only known 444G (a mis-stamped Outfitter) is an 18" 'Ballard'.
All newer Model 444 barrels (no 'S's, post-move, ~April, 2011) were 22" 'Ballard' and massively inconsistent in nearly every way. (2011-2012)
When Remington resumes production of the Model 444 (no 'S's), they will again be using 22" 'Ballard' barrels (1:20").
I hope that clears things up...
**(I ignore Marlin's ongoing attempts at convincing customers that their rifles actually have 18.5", 20", 21.5", 22.5", or 24" barrels, because the hood that extends into the action is not included in LEGAL measurements of barrel length. As such, it's a
lie, in my opinion. The
legal barrel lengths of Marlins lever guns are about 1/2" shorter than advertised. -Depending upon model, year, production batch, and variant.)