I don't understand why you need to prove your husband is in L1 status for the H1b application. Rather you should focus on proving your eligibility for H1b classification.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.
Whether your husband is in L-1 status really has no bearing on your status as a L-2. True, your husband is the principal so if he was not in status neither would you. A copy of your husband's L-1 receipt notice/approval notice would be ideal. You need to consult with an immigration lawyer to further bolster your H-1 position. The evidence all goes to the type of position, the prevailing wage offered, your education and other credentials. I suggest you speak with an immigration lawyer if you have concerns.
L-1 is an employee of U.S. corporation and must be paid in the U.S. If you seek COS, IO may seek status documents by issuing an RFE. If you are unable to document, COS will be denied, but if all other paperwork is good, the petition may be approved; in which case, you will consular process. If the question of status came up in an RFE, be prepared to answer this query at the visa interview.
This response is general in nature and cannot be construed as legal advice, given that not enough facts are known. Any comments offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship. If you would like additional information based on this response, please contact my office at 510 657 7665 or 415 902 0832 to schedule a consultation.