Hello Wayne,
Maybe a little bit late, but it is always possible to retrieve the date of booking.
When an invoice is posted, the data is written to ar_mstr.
Every Financial booking is traced with batches.
To retrieve the book date and the related userid, retrieve the ba_mstr.
In the ar_mstr use the field ar_batch.
Retrieve ba_mstr where ba_batch = ar_batch and ba_module = "SO".
The ba_date is ALWAYS the system date of booking.
William W