I am looking for some help on the Doctrine of Optional Completeness.

I have a set of business records to indroduce through a business record affidavit and the document is missing page "2 of 2" because the business doesnt keep records of that page because it is not an operative part of the customer's contract. However, all of the pages indicated on the affidavit are there.

I anticipate an argument that they are not admissible based on this doctrine. However, this doctrine just says the oposing party "may" introduce the remainder of the document if the partial document would mislead the jury.

Does anyone know of any caselaw on point or any other doctrine that might by harmful or helpful?

Get a copy of that page from one of their new contracts to see how it relates to the pages you do have. Maybe consider having the custodian come testify about this other page to help explain its insignificance.

Most of the time that I've seen pages not kept as part of other business records its because the page is torn off and given to the customer. The missing page may be interchangeable with that page on all of their contracts so if its omission could be misleading I don't see why the defense can't just offer that generic page as well under optional completeness.

Optional completeness is a remedy for the party against whom a portion of the document is offerred, not a prohibition on the admissiblity of the part the proponent seeks to admit.

RULE 107. RULE OF OPTIONAL COMPLETENESS
When part of an act, declaration, conversation, writing or recorded statement is given in evidence by one party, the whole on the same subject may be inquired into by the other...

Your bigger issue might be that the face of the document displays a lack of trustworthiness because of the missing page:

Records of Regularly Conducted Activity. A
memorandum, report, record, or data compilation, in any form, of acts, events, conditions, opinions, or diagnoses, made at or near the time by, or from information transmitted by, a person with knowledge, if kept in the course of a regularly conducted business activity, and if it
was the regular practice of that business ctivity to make the memorandum, report, record, or data compilation, all as shown by the testimony of the custodian or other
qualified witness, or by affidavit that complies with Rule 902(10), unless the source of information or the method or circumstances of preparation indicate lack of trustworthiness.

I would have a custodian or other person familiar with the business practices available to explain the absence of the record as being the normal course of business and have the missing page, if it can be located, to explain the absence. The record may be self authenticating under 902(10), yet be found to be untrustworthy under 803(6).