Understand what the bar tests
Services work is judged on delivery against someone else's specification; GCC roles are judged on ownership of a product area over time. Panels probe what you decided, what you rejected and what happened afterwards. Candidates who can only describe requirements they implemented struggle in precisely this part of the loop.
Translate out of project language
Client names, engagement durations, allocation percentages and delivery-manager vocabulary tell a GCC panel very little. Rewrite the same work as products, users, systems and outcomes: what you built, who used it, what it changed. This translation converts more screens than any additional certification will.
Prepare for a distributed loop
Expect more rounds than a local interview, several with the parent company's engineers across timezones, and an explicit look at how you work with people you rarely meet. Evidence of asynchronous collaboration, written decision-making and progress made without waiting for a manager is directly relevant here.