[jagusafr]

Any idea whether “He descended into hell” was added to, or removed from, the original?

[Campion]

You're thinking of the Apostle's Creed, which was the baptismal creed of the Roman church. Different, and much shorter, creed.

The line "he descended into hell" in Latin says "he descended ad infernum," which translates as "to the nether regions". It's a reference to the "preaching to the spirits in prison" (the righteous who died before the resurrection, in other words) mentioned in 1 Pt 3:19.