ACAT/cost basis/tax question

This may be a simple question, or may be complicated. In any case, I have not been able to find a good answer on my own. The scenario is as follows:

I had a collection of stocks at Vanguard. Some of them were sold for significant loss from there. Other assets were transferred through ACAT to Webull, having depreciated substantially. Cost basis was not reflected accurately in Webull, and my understanding is that cost basis is not even transferred through ACAT.

Now, when I ultimately sold these assets in Webull at a substantial loss, is the cost basis come tax time going to be accurate and based on initial purchases at Vanguard? What are the chances I have to manually change a lot of information?

TIA