A number of folks shoot unlubed bullets at target velocities on purpose and find the leading no worse than with lube. Lead alloys are pretty slippery against steel. If you don't push them very hard and your bore is smooth, it seems to work OK.
If you have one or two unlubed bullets, there will be enough residual lube in the bore from the lubed ones that went before it that they should have plenty of lube. The concern that they may have missed sizing, too, is the larger one. It won't do a lot to pressure to fire an unsized bullet (many find they shoot more accurately than sized bullets do from some molds), but the fatter bullet can bulge a case enough to cause a feed failure in some chambers, so you want to plunk test the rounds to see if you run into a problem.
If you were shooting cast bullets toward jacketed rifle bullet velocities, that's another issue, and I would want every bullet carefully lubed with the best lube I had. For handgun loads, even magnum ones, if you are really concerned, just rub the sides of the bullet against some paraffin wax (a candle will work). For just one shot fired between lubed shots, you don't need the perfect lube to be present.