How to communicate missed timelines due to engineering misalignment without throwing the team under the bus?

Hey PMs, I’m dealing with a situation at work and would love your perspective. I recently had to shift timelines on a project because we missed our initial estimates. The product depends on a new dataset that another team is still collecting and structuring. In parallel, my team was supposed to start building the architecture using mock data. I provided sample data (~1GB) and encouraged the team to proceed with mock data so we could make pro