Compare 2 Dates For Month Differences

I need to compare dates from two workbooks. The dates are not entered in the same format. In order to compare them I store them in Date variables.

However, some dates entered do not have a standard date format (for example, day is missing) and I get an error when I try to store them in a Date variable.

The solution I thought out (most likely a bad one) was to temporarily re-dim the variable from Date to String when an error occured. The macro would then be able to store the incomplete date and do the comparison.

So, basically, the variable would be dim'ed once as a Date, then possibly dim'ed a second time as a String, and if this occurs, then it would be dim'ed back to a Date once the erroneous date would have been treated as a String.

My problem is that it doesn't appear to work if I use the dim statement because of "duplicate declaration in current scope". Is there a way to re-dim a variable as something else within the same macro?