When the degree to which a given set of statistics is a good representation of the current table demographics is under scrutiny, I often experience that people rely solely on the collection date.
Some tables will not have Teradata stale statistics even if you never refresh them. Just think about pretty static lookup tables. Various changes can occur for other tables, with some fields having ever-expanding value ranges and others having a constant share of only a few codes. How can you get a better picture of statistics and determine if they are stale? There are several possibilities. Maybe the easiest could be to just run a simple query on the table and use a WHERE CONDITION on the column, which should be tested.
SELECT * FROM TABLE WHERE TEST_COLUMN = ‘X’;
Compare the number of estimated records (you can see this number in the Teradata Administrator) with the number returned, and you will know if the statistics are stale.
Note that you cannot expect the optimizer to be next to the individual row on any occasion. Still, the divergence should not be more significant than a small one-digit percentage, depending on the overall table size.