"Hard drive cable A1278 model 821-1226-A instead of 821-0814-A"に関する回答They are different lengths, although some places will sell you the same cable for these two different part numbers. 821-0814-A is longer than 821-1226-A. I advise using the correct cable as extra stress on the cable will most likely mean it doesn't last as long as the correct one.
"Using a hard disk cable meant for a different model"に関する回答If you're desperate, you can make the short one reach if you don't use the two 3mm screws that hold the middle of the cable down. I wouldn't advise it. I did it but it failed eventually after a couple of years. 922-9771 (821-1226-A) is too short. Use 922-9062 (821-0814-A) because it is longer.