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 lookup tables which are quite static. For other tables, various degrees of changes can occur, with some fields having ever-expanding value ranges and others a constant share of only a few codes. How can get a better picture about statistics and find out if they are stale? There are several possibilities. Maybe the easiest could be to just run a simple query on the table and using 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 real number returned and you know if the statistics are stale.
Note that you cannot expect the optimizer to be right down to the individual row on any occasion, but the divergence should not be any larger than a small one-digit percentage, depending on the overall table size.