So here is my grand theory (if I understood the question correctly):-

Angier was Lord Coldlow from the very beginning. He just pretended to be the American Robert Angier, to spare his family the embarrassment of his theatrical career. So existence of Lord Caldlow is clear.

Later on the day of the accident, Angier called spectators to check the machine. Borden came and examined. Given the fact, they knew each other the best, we can assume Angier caught him right then when Borden was on stage to check the machine.

So when Angier understood the right time has come, the time he has longed for a long time, he did not turn the machine on simply i.e. no extra copy of him was made on that day! But he tried to befool the viewers by the sparks of the machine and all that, but it was not really working like other days. So the existence of Angier remained as Lord Caldlow (whom no one identified as him) and Angier could make Borden his murderer by killing the present in the centre copy of himself. Simple yet a compact plan!

So here is my grand theory (if I understood the question correctly):-

Angier was Lord Coldlow from the very beginning. He just pretended to be the American Robert Angier, to spare his family the embarrassment of his theatrical career. So existence of Lord Caldlow is clear.

Later on the day of the accident, Angier called spectators to check the machine. Borden came and examined. Given the fact, they knew each other the best, we can assume Angier caught him right then when Borden was on stage to check the machine.

So when Angier understood the right time has come, the time he has longed for a long time, he did not turn the machine on simply i.e. no extra copy of him was made on that day! But he tried to befool the viewers by the sparks of the machine and all that, but it was not really working like other days. So the existence of Angier remained as Lord Caldlow (whom no one identified as him) and Angier could make Borden his murderer by killing a copy of himself, the then present person in the centre. Simple yet a compact plan!

So here is my grand theory (if I understood the question correctly):-

Angier made a copy of himself a long time ago and set him up as Lord Coldlow. Now certainly setting his copy as a lord have definitely taken a long time. So we can conclude this copy was made after he realized how Borden had duped him. So he made a master plan and made a copy of himself and planted him as Lord Coldlow after he returned with the machine.

Later on the day of the accident, he called spectators to check the machine. Borden came and examined. Given the fact, they knew each other the best, we can assume Angier caught him right then when Borden was on stage to check the machine.

So when Borden understood the right time has come, the time he has longed for a long time, he did not turn the machine on simply i.e. no extra copy of him was made on that day! But he tried to befool the viewers by the sparks of the machine and all that, but it was not really working like other days. So the existence of Angier remained as Lord Coldlow (whom no one identified as him) and Angier could make Borden his murderer. Simple yet a compact plan!

So here is my grand theory (if I understood the question correctly):-

Angier was Lord Coldlow from the very beginning. He just pretended to be the American Robert Angier, to spare his family the embarrassment of his theatrical career. So existence of Lord Caldlow is clear.

Later on the day of the accident, Angier called spectators to check the machine. Borden came and examined. Given the fact, they knew each other the best, we can assume Angier caught him right then when Borden was on stage to check the machine.

So when Angier understood the right time has come, the time he has longed for a long time, he did not turn the machine on simply i.e. no extra copy of him was made on that day! But he tried to befool the viewers by the sparks of the machine and all that, but it was not really working like other days. So the existence of Angier remained as Lord Caldlow (whom no one identified as him) and Angier could make Borden his murderer by killing the present in the centre copy of himself. Simple yet a compact plan!