$Revision Not Showing All Dates Revised

I have an application that uses an old lockout process (developed in R4). When a document is put in to edit mode, code in QueryModeChange sets a Lockout & LockoutDate field and saves the document. If another user tries to edit the document, they get a message.

When the document is put into lockout, the date Modified in the document properties box changes. And the users name is added to the $UpdatedBy field. But, the $Revision field does not show this date.

Since the document is saved, shouldn’t $Revision show the date/time of the change?