I can't tell you anything about serial number prefixes because I put my .44 together. It's not factory original. It is one of the older barrels. When it was a .44 Mag. all I shot in it was Hornady LE ammo, and it shot fine. Tim reamed it to .445 for me and slugged it. Since then, I've been using a .445 Super Magnum load with Montana Bullet Company's 240 gr. .433 Gas Checked Semi Wad Cutter. They're not a cheap bullet, but they shoot well being pushed to near 2000 fps. I may, one day, buy a standard size barrel, but I won't get rid of this one. It may be over sized, but it shoots.
If I were doing the buying, it wouldn't matter much if it were the older barrel.....if the price was right. Either shoots....just depends on what ya feed em.
Pete