Hi Tim,
I think I know where you're coming from. While working with validity dates and their comparison, I've wished BRF+ provided a more convenient way out.
As such, you cannot use the same column as a condition as well as a result column at the same time. However, one workaround would be to use intermediate variables which would hold copies of your context (or condition column values) values and have these specified as the result columns in your decision table. Yes, this is not an elegant way to do it.
Probably a more elegant way (and which I've used before as well) would be to use a combination of a decision table and a table operation. So, in the product example you've given, you could make PRODUCT and TERRITORY as the condition columns and the rest as result columns. Then, in your rule, you can call the decision table and receive a table of results (for the input product and/or territory) from it and then do a table operation (in which you can write comparison conditions) on the results to get the valid records.