I thought there were three incomplete down clues, but luckily only two!
19 down: Record verse penned by young prince (7)
Letters (A - C* - I - E
So ARCHIE
16 down: Reportedly favour one marine creature - or another?(4,4)
Letters: - R - Y* - E - L
CRAY, but will have to go through alphabet to complete the second part
.. and possibly hchange the first ...
* Y from archery'
*C from 'archery'