英语语法 虚拟语气：非真实条件句.should 是什么?

英语语法 虚拟语气：非真实条件句.should 是什么?
第一个should + have + done
You should have seen his face.(原句)这句是省略了从句,没错吧.
If the steamer should have left port at noon,it will be passing through the canal now.（原句）
不应该是:If the steamer had left port at noon,it would have been passing through the canal.
或者：If the steamer left port at noon,it will be passing through the canal now.
请指教上两句对吗?原句中的should have 那么最上头那句也不理解了.
第二个 should + be
If you should see Celia,give her my best wishes.(原句)
不应该是：If you saw Celia,give her my best wishes.
第三个 作表语
They suggested that we should meet at the station.(原句)请问有点像had better的感觉,没有时间的概念,也是非真实条件句吗?
suggest有这个短语呀 那么这样呢
It is desirable that everything should be ready by five o'clock.(原句)