Here in the printer’s manuscript, Oliver Cowdery initially wrote “yea & it was which wrought miracles” in verse 16, which makes no sense. Later, perhaps when he proofed 𝓟 against 𝓞, Oliver crossed out it was and supralinearly wrote even all they (the ink level is slightly heavier). He probably wrote it was because of the preceding occurrence of those words in verse 15 (“behold it was the faith of Ammon and his brethren”). 𝓞 is not extant here in verse 16, but it probably read as corrected in 𝓟.
Summary: Maintain in Ether 12:16 the corrected reading in 𝓟, “yea and even all they which wrought miracles wrought them by faith”.