Mostly evidence work. Retrieving payroll from a retired system, obtaining certified copies of transaction documents, translating agreements executed abroad, and having counsel read the corporate chain all take chargeable time that a straightforward internal move would not require.
Scope the corporate review as its own item
Ask for the relationship analysis to be quoted separately, because it is the part most likely to expand once the deal papers are read. Confirm what happens if the review shows the relationship does not qualify in its current form. Government charges should be confirmed at the relevant step rather than estimated now.
Deciding early how much retrieval is justified prevents open-ended spending on records that may not be needed. Add one further question to that separate corporate quote: what happens if the review concludes the relationship does not qualify in its current form. Sometimes the answer is a restructuring the group would be willing to undertake, sometimes it is a different applicant, and sometimes it is that the transfer cannot proceed as planned.
Each has a different cost and a different timeline, and establishing them in advance keeps the finding from arriving as a crisis. Hypothetical example: a printing group's corporate review identifies an intermediate holding company that breaks the chain, and because the possibility had been priced beforehand, the group can weigh a corporate change against a different route within a fortnight rather than spending that fortnight deciding who should pay for the answer.