The control terms. The service agreement should state that the petitioner assigns, supervises and evaluates the transferee and can withdraw her, and that the work is tied to the petitioner's product or process. Settling this before filing avoids a request for evidence that can cost months.
Negotiate the control language first, then file
Timing on an offsite L-1B case is driven less by USCIS than by the client contract. A statement of work drafted for commercial purposes typically says nothing about supervision, and a client's standard terms may even assert day-to-day direction over contractor personnel, which is exactly what the petition must disprove. Hypothetical example: a Sainte-Brigitte-de-Laval engineering firm agrees a deployment with a U.S.
manufacturer and files the petition before the contract is finalized; the signed contract later gives the client authority to direct all onsite staff, and the request for evidence that follows delays the start by months while the parties amend it. The correct sequence is to agree control language with the client, sign, and then file with the executed agreement as an exhibit. Meanwhile, confirm the qualifying year and corporate relationship, assemble the technical evidence, and decide on premium processing.
Build the client's go-live date backwards from a filing date that leaves room for one round of additional evidence.