Just note that if the values in A2 and B2 are really date entries, and not text entries, then this will return: 43831-43845
which is the numeric value of the dates (that is how Excel sees them, the number of days since January 0, 1900).
That is why I applied the TEXT function to each value, to get it to show the format you expect.
It looks like you also blended both Concatenate actions, i.e. it is typically written: =A2 & "-" & B2
To use both "CONCATENATE" and "&" in the same formula is redundant and unnecessary.
No worries Alan! I have them myself (especially on Monday mornings), but I cannot blame it on my age (not quite there yet).
It feels like I have gotten "dumber" since having kids (I blame it on lack of sleep).