Evaluate ( Get ( LayoutTableName ) & "::ID" )
So simple, it hurt! Thanks!
Get ( RecordNumber ) returns the position of a record in the current found set. If this is the last record in a found set of 5 records, it returns a 5. Sort the records differently so that it is the first record, the same function for the same record will return a 1.
Get ( recordID ) returns an internal serial number FileMaker assigns to each new record at the time the record was created. You could use this value to find the record in the specified table, but you'd have to either add an calculation field with Get ( RecordID ) as its calculation so that you can perform a find or loop through records checking the result of this function until it matches the value save in the help ticket.
And while Get ( RecordID ) looks like a useful alternative to defining your own ID field using an auto-entered serial number or Get ( UUID ), it's not a good idea to do so: Why Record ID's should not be used as Primary Keys in Filemaker Relationships.