dantheman
Bah humbug
No errors except for your maths644+72 is not 816 at least not here in Germany
However I'm not sure if Sooty Tern should be included between those regular species. It's not an annual breeder and very scarce and not easy to get even then
But you list 57 annual or near-annual species but you believe they'll only get 34 additions out of these?
Maybe they will get only around 35 out of these but then there are still those real rarities which are not included in your number. Don't forget, they have scheduled almost all autumn for vagrants and have spare-time in December. I believe 770 is more likely. At least if they are committed to it.
Somewhere between 740 -780 (880) then
It kinda depends on whether it is a good autumn for vagrants and whether the birds fall where they are, or how committed they are to travel/twitch? etc
(Not forgetting the recent ABA Big Year, when expectations from this forum were generally exceeded.)