>>24620065
I assume you mean the table here.

https://en.wikipedia.org/wiki/Latin_phonology_and_orthography#Ecclesiastical_pronunciation

You're right about what the table says (I don't see if it cited a source), but consider the Liber Usualis cited below. It says "each vowel has one sound." However, it is a guide primarily to singing, not speaking, and it's mostly concerned with warning Americans not to inadvertently use English vowel sounds or diphthongize vowels.
http://www.musicasacra.com/pdf/liberusualis.pdf