The lambs heart isn't something we eat every week, it was a one off.
He'll now eat a few bites (say 2 or 3 pieces each 1cm square, very thinly sliced) of lamb or chicken, no crumb, just like mine.
Sprats are a winner, he's had them a few more times and eats 1.5 - 2 full ones (and they are quite big really), he makes the fish sound just before eating them
Garlic prawns, no crumb, will eat about 2 - they have to be fresh raw prawns that I cook, not the pre-cooked wet tasteless ones.
He is still rejecting pan fried smoked sardines. Doesn't even acknowledge they are on his plate.
All in all there is steady progress. Every now and then he still gets a fish finger or sausage if I feel like he's been several days without a decent bite of protein but he will also take eggy bread for breakfast most mornings now which means half an egg (or up to a full egg) going in, so I am far less concerned about his protein.