Some of the work those other companies did could have been wipes/dissolves.
And I think some of the lasers were also done by Peter Kuran, who would later form his own company, which was given a lot of the lightsaber animation work in Jedi. I have a Cinefantastique issue with an interview of him, let me check that sometime.
Yeah, Peter Kuran was one of the animators working under Adam Beckett. Beckett was essentially the one responsible for the work but he had of course a team of animators under him. Anyway, I found an old interview where Beckett mention Barry Nolan at Van der Veer Photo Effects being responsible for the lightsaber effects just like you said. So that's at least two companies responsible for the optical lightsaber work on the first film.
Haven't checked what work Ray Mercer & Company, Modern Film Effects and Master Film Effects did on the film. It's likely they did wipes and dissolves like you say. Mercer, Van Der Veer and Modern effects all did work on ESB too.