Although it was suggested in a few DL exercises to use the indefinitive article to imply the regular frequencies of time, day, month, etc, it is better that one use "ogni" to mean "every", i.e. "ogni giugno" so to avoid ambiguity.
For more esempi, please visit this webpage - https://mobile-dictionary.reverso.net/english-italian/in
No "in giugno" is not different from "a giugno." In and a are largely interchangeable. A is more casual and preferred in the South. See this article: https://www.thoughtco.com/italian-vocabulary-italian-calendar-months-4087628
I had the same question.
It is because they distinguish between arrives and comes, although they mean almost the same thing. I definitely think that it would be correct if a person were checking it, but it is only a machine- very technically oriented. Sometimes too technical.
Guillhez and wshvet: True and July is named after Julius Caesar; if only he were called Gulius we'd probably have Guly....yes, Augustus gets us August, even if he was born Octavio. October was already claimed as the 8th month before adding the extra two to give us 12! 10Sep15 (yeah, September was the 7th month and November the 9th..go figure!)