Would you mind explaining the difference between industrial vs trade union? Would something like the janitorial staff of a building owned by a gaming company be covered in an industrial union?
Industrial unions organize by shop; craft unions organize by trade. Industrial unions have much greater leverage because they can (theoretically) change conditions for the entire workplace, not just for one group of workers in the workplace. Historically, this meant, for example, organizing everyone in the auto factory in one union as “auto workers” instead of having machinists in one union, engravers in another union, mechanics in another, etc.
Ask Google about "difference between industrial and craft union".
There's US labor history involved. The AFL-CIO was formed by a 1955 merger of the American Federation of Labor and the Congress of Industrial Organizations. The AFL was the umbrella organization for the craft unions - electricians, plumbers, etc. The CIO was the umbrella organization for the industrial unions - everybody non-management in an auto plant, everybody non-management in a steel mill, etc. That's what "wall to wall" means.
Agreeing on the bargaining unit is a major issue in employer-union relations. A "wall to wall" agreement avoids internal issues over who can do what job. (Is plumbing for compressed air a plumber or a steamfitter job?) That helps the employer. But it gives the union more leverage over the employer because the union has all the employees.