Whether an Excel expression can be converted to the array form is sometimes hard to predict. For example, the following screenshot shows a table with a row of dates at the top, followed by four rows that reference the first. The first three (i.e. Excel rows 3, 4, and 5) each contain an array formula. The first two are fine, but the third, using EOMONTH(), breaks. Then Excel row 6 shows the same EOMONTH() formula, but in non-array form. It works fine. In B3:B5 and C7:I7 I've used FORMULATEXT() to display the functions in the various rows and cells.
I don't see anything obvious in the documentation for EOMONTH() that would predict the failure.
Is there a way to figure out which functions have this kind of limitation? (This is ostensibly the general form of my question, but it doesn't really help much).