I don't think so... It's already very formal. I'd add a worden if it's meant to go into a juristic/technical direction, to make clear this desired part of the contract was fulfilled, but actually leaving worden out already makes it as formal as I think it can get.
Die Leistungen sind .. erbracht worden.
Die Leistungen wurden erbracht.
The way you put it first is grammatically correct. It is a form that sounds slightly poetic and aloof, having been used in historic dramatic poems or such.
Die Leistungen sind erbracht.
It's a bit like saying "It was I" instead of "It was me."