Given your two formats in your example, 12/06/30 is a valid value in both date formats. So there is an ambiguity if you want to get the 'true' date.
It's always a good thing if your input data is in a well defined format, so if you can get your users to use one format, that would be much better than guessing around when reading in, right?
If possible, use a four digit year format. QV will use some AI to determine the full four digit year (e.g. determine 2013 from 13). I believe it will interprete 63 - 99 as being in 20th century, and 0 to 62 in 21st century (range is +-50 years from today).
Maybe this is according to what your users expect, maybe not.
And finally, there is an ISO standard for dates, which avoids the DD/MM/YY(YY) resp. MM/DD/YY(YY) etc. ambiguity altogether: 'YYYY-MM-DD'
This kind of issues occur whn working on Excel sources, u have gt lots of expert advices,
I have my HR analysis partially dependent on excel files, my personal experience says put the blame on the users and demand them to follow one file / column format, tht is the only option u have with u
or else u work on it andf stable the files once received atleast for date column issue.