A.T. Robertson Commentary 1 Corinthians 16:17

"And I rejoice at the coming of Stephanas and Fortunatus and Achaicus: for that which was lacking on your part they supplied." — 1 Corinthians 16:17 (ASV)

At the coming (επ τη παρουσια). At the coming here of Stephanas, etc., the very word used of the παρουσια of Christ (15:23).

That which was lacking on your part they supplied (το υμετερον υστερημα ουτο ανεπληρωσαν). Either "these filled up my lack of you" or "these filled up your lack of me." Either makes perfectly good sense and both were true. Which Paul meant we cannot tell.