I'm thinking the best solution is to just change the CSV format to.
date,retailer,upper_tier1,price_tier1,,upper_tier2,price_tier2,upper_tier3,price_tier3
Then use a similar method as you suggested. That will allow me to use temporal lookups without worrying about changes in the number of tiers. If they add additional tiers I will just have to change my searches.
Thanks again for the assist.
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