As site coating inspector, the incidents like lack of part B have been encourntered for several times on both my and my colleague's projects. We have been doing like this:
1. Use hard plastic scraper to remove the wet part A as more as possible, this can minimize the use of solvent which may cause danger.
2. Use white rags satulated with solvent as advised by paint maker, and with brushes where necessary, to remove the traces of part A as more as possible.
3. Maybe the steel is already very clean under naked eyes, we still prefer to reblast the affected area with abrasives, which may only need for short time operation. We believe it is safer and can eliminate the potetial risk.