There didn't need to be two electoral slates. There just had to be Pence's "reasonable" position that a slate of electors was contested, and then just eliminate them from the total count. The Constitution doesn't say how many electors make a full slate. It just says the VP needs to decide that the full slate has been presented, and then tally the votes. There is a perfectly reasonable case to be made that - if election fraud was widespread in a state - that Pence could simply rule those state's slate of electors invalid, and eliminate them entirely from the count. That's the dastardly simplicity of the plan... it adheres to the LETTER of the law, without respecting the INTENT. Which is how Republicans get ALL their business done. So this is common practice.