Transforming 6 digit integer to a date when bad values are involved

I have a dataset with chunks of bad data in it. To get a MFG date I pulled the first 6 digits of the serial # to get a "date" in an text format.

if the data is correct it should read out the correct date, but in some cases the data will have 06B378 or other letters or texts that should not be in there. How would I go about excluding the bad data as well as converting the good 6 digit data into a date format?

Let me know your thoughts or how I go about this. I tried to alter columns to integers and inherit bad values as null but it seems to not be catching all bad values.

Thanks