Ok...

Both of these formulas are array formulas**.

Use a separate cell to get the total count of tail numbers that meet the

criteria.

Date = named range for your date column

TN = (Tail Number) named range for the acft tail numbers

Count of distinct tail numbers for the month of 5 (May):

=COUNT(1/FREQUENCY(IF(MONTH(Date)=5,MATCH(TN,TN,0)),ROW(TN)-MIN(ROW(TN)+1)))

Assume the above formula is entered in cell G1.

Formula to extract distinct tail numbers:

=IF(ROWS($1:1)<=G$1,INDEX(TN,SMALL(IF(MONTH(Date)=5,IF(MATCH(MONTH(date)&TN,MONTH(date)&TN,0)=ROW(TN)-MIN(ROW(TN))+1,ROW(TN)-MIN(ROW(TN))+1)),ROWS($1:1))),"")

If the first row of your ranges is set and will not change we can shorten

this a little. For example, your posted formula uses references to ranges

that start in row 2. In the above formula we calculate an offset from the

starting row so that this formula can be used by anyone. In other words,

it's generic. We can shorten it a little by hardcoding this offset rather

than calulating it. So, if the data ranges start on row 2 we can this

version:

=IF(ROWS($1:1)<=G$1,INDEX(TN,SMALL(IF(MONTH(date)=5,IF(MATCH(MONTH(date)&TN,MONTH(date)&TN,0)=ROW(TN)-1,ROW(TN)-1)),ROWS($1:1))),"")

** array formulas need to be entered using the key combination of

CTRL,SHIFT,ENTER (not just ENTER)