I don't know how hard what I'm asking for is, but I've had some fun
today tracking down "undetermined" variants in sets that I have from childhood.
I'm pretty close to mining it as far as I can go, but I would certainly
consider parting out some sets from eBay with the added interest in finding the
variants. Could we have a tool that would just identify a list of sets that
contain a piece of undetermined variant?
[...] To access this feature, simply go to the Advanced Catalog Search page: (URL) and click "Show More Options". At the bottom of the first row of additional options there [...] (68 months ago, Oct 30, 2018, to Suggestions)