If I amend a previous year's return, do I need to include all of the wages and W2's from the original return?

For example, I never thought to add the 1098-t forms to the previous 3 years. Can I add only the American Tax Credit to my amended returns, or do I need include all of the same wages as before?

your revised tax return must be a true, complete and correct tax return.

1040X reflects any differences there compared to your original, and becomes your new tax return.

How to file:

Do not include your old 1040 nor your revised 1040 because the Form 1040X reflects any changes there and becomes your new tax return.

Include any new/corrected document only if it shows federal tax withheld, and include in order only those Sequence Numbered tax forms and Schedules that changed or were added due to your amendment. 

Attachment Sequence Number is on all the forms and Schedules that come after 1040.

Mail to the address shown for your location in the Instructions for Form 1040X.