could vs Could have by then

Some examples from the web:

• Each delegation could reasonably comprise 12 members.
• I could find electrical work, you could landscape.
• You could be American-Italian; you could be American-Irish; you could be British-Pakistani.
• You could say something... that could reveal your location or his.
• How could I thought I could leave unharmed...
• It could double the amount of weapons we could bring online.
• We could... well, you could forget your life in this place.
• I could send for another horse... and we could ride together.
• If we could dream it, Simon could build it.
• Only the persons who could locate the Dragon Tomb could share this country with me.
• It could be exhaustion, or you could have a summer flu.
• They could create massive storms that could scuttle any landing attempts on the beaches.
• It could give us reasonable doubt if I could just suggest to the jury...
• Then you could shoot me and I could sleep.
• We could forge a real alliance that could last generations.
• He could seal his prisoners in there and no one could hear them scream.
• I could never separate myself from the job like you could.
• Nothing Scrooge could do or say could stop the relentless march of those terrible bells.
• Perhaps you could have him call me and I could explain the legalities.
• That she could sniff it out when nobody else could.

Some examples from the web:

• The teacher could have been anything by then.
• It would be desirable to introduce these limits before 2012, as the pollution of residential areas and air pollution in general could have escalated considerably by then.
• They could have easily eaten seven zebras by then.
• By then, I mean, he could have forgiven me.
• No way he could have gotten clear across town by then.
• By then, other officers responded.
• I want Matobo found by then.
• The trial should be over by then.
• We should know for sure by then.
• But by then cattle were already raised unnaturally.
• Our antimatter supply will be depleted by then.
• Then I wished to go back, but by then...
• Then let's at least hope you find the bomber by then.
• Think you could have some patent-ready diagrams by then?
• Alberto was 80 years old by then and he could have rested at last, proud and satisfied with the goals he had reached with his tenacious work, besides enjoying his fortune.
• Okay, what if I told you that I could have a new book for you by then?
• Steve will be home by then, and then you could talk about whatever it is that's bothering you.
• Then he can fight it in court, and he'll likely win, but the election will be over by then.
• And then he tried to sell digital cameras, but by then it was too late because everyone had one in their phone.
• And then they started asking me questions about myself but by then I was Consuelo.