WhilePrintingRecords is just a tag to tell CR when you want something done, CR reads the data a couple of times, then formats the report. Most of the time this is when the data is available.
If you can't see the table that you want in the database expert, CR isn't going to be able to find it.
What do you see when you run the formula? I guess a date, quite possibly 1/1/1900. You declared a variable and then displayed it, you never set it to a value. If this is a field in the dataset that you want to use the formula would look like:
{table.wo_estcomp}
that would print the value of the table.field
HTH