I reread the inscription in this question about the abbreviation D. O. M. dated to 1749:
The variation between I and J caught my eye. It seems to me that:
- J is used in all consonantal positions.
- J is used in hujus.
- J is used after I: varijs, munijs, junij.
- In all other positions I is used, whether it is (classically) short or long.
U and V behave in a similar way: U is used in all vocalic positions, V in all consonantal ones. The only (perhaps) exception is that after Q we always have U.
The spelling choices seem very consistent, so I can't attribute this to chance. This seems to suggest that the U after Q is pronounced as a vowel, and the J in hujus, varijs, munijs, junij is pronounced as a consonant. Is this conclusion justified? All other make sense to me, but varijs, munijs, junij sound weird to me. Is it indeed a matter of spelling convention where no two consecutive Is can appear.