Most brands discover what they own on the day they try to leave. Do it in the other order.

What you probably own

If your agreement says the formula is yours, you own the formula: the list of ingredients and their percentages. That is less than it sounds.

What you probably do not own

The master batch record. The order of addition, the temperatures, the mixing speeds and times, the hold points. This is the actual manufacturing knowledge, and it usually belongs to the factory.
The raw material specifications. Which grade of which ingredient from which supplier, at which particle size.
The stability and challenge test data. Often held by the lab, not by you.
The component tooling. If the factory paid for the mould, the mould is theirs.

A formula without a batch record is a recipe without a method. A competent new manufacturer can reverse-engineer it, but that is six to twelve weeks and a fresh stability study you were not planning on.

The eleven documents to have in hand

Signed formula with exact percentages and supplier grades
Master batch record, including the scale-up notes
Raw material specifications and current suppliers
Certificates of analysis for the last three production lots
Full stability data, including the packaging compatibility study
Preservative efficacy (USP 51) results
Component drawings and specifications
Artwork files and the approved label copy
For OTC: the SPF and broad-spectrum test reports, and the drug listing
Any claims substantiation you paid for
The current quality agreement

Ask for these while the relationship is good. Ask as part of an annual file review, not as the first sign that you are shopping.

Then plan the overlap

Never let the old run be your last run. Order enough inventory to cover the new manufacturer’s full development and first-run timeline; for a cosmetic that is roughly five months, for an OTC closer to seven. Brands that skip this end up back with the factory they were leaving, on worse terms.