Combining batches? I would never offer to do that.
...DIY plating process using the Caswell System on a 1967 911.
https://youtu.be/hTupOgImpWo
Well, there's combining batches, and combining batches. I've seen an entire car's worth of minutia, seemingly hundreds of bolts, nuts, washers, etc. for which cataloging such parts would be difficult for one car, let alone two. But, sometimes depending on what's being done, you can successfully combine and people can work together and save.
I did that twice. One time, the part to be plated was my automatic transmission filler tube; the original was damaged by a mechanic who didn't double wrench the fitting at the transmission. The OEM replacement from MBUSA was not plated as original, but painted black. The second set of items was the parts around the trunk (boot) lock/latch.
Friends working together to help each other.
Now, two cars worth of miscellaneous hard to categorize or separate bolts and nuts? No, too difficult to keep them separated.
All this plating involves really nasty chemicals. Putting it down the drain, on the street, in the woods, is a toxic and environmental no-no.