Starting the books
The opening figures a company already trading brings with it, loaded in order and compared against the system they come from.
The order is not a suggestion: parties before payables, products before stock, everything before the trial balance. A stage already loaded cannot be loaded again.
Each stage posts against Migration Suspense, so that account is zero exactly when the loaded figures agree with each other. Do not name it here — it is already the other side of every line.
Every lot arrives with its own unit cost. A quantity alone makes the first sale of that SKU produce a meaningless margin, so a lot without a cost is refused rather than loaded at zero.
Six figures that must match the system being left, line by line, plus the acts no report can assert. Type what the legacy system says.
Both systems for the same period, account by account. A difference with a written reason is a finding; one without is an unfinished migration.