Your date fields I would expect be created in the table bound to your form. If you want to get the field in your query then if possible add the table that the form is bound to; to your query using a related field to make a join(union) .
If a relationship exists between the 2 related fields then you will see the join immediately on those fields otherwise the 2 ID fields will show joined. This may not be what you want, so right click the join (exactly on line) and select delete to break the join.
Then once you decide which 2 fields you want to join, click on one from the list and drag it over to the other to connect the 2. Then Right click on the line until you see "Join Properties" and select it. Read the options and select what is appropriate for you. generally you would choose to see "All" (Main table/Query) the records from one and only those that match from the other.
By doing it this way the date fields will be available in your query. the safest way is to copy or start a new query and experiment to see how the results change. If you duplicate an existing query that is currently bound to the report, it will simplify things because you just have to tag the fields to the end. Double check the 2 joined fields to ensure they are returning equal values.
Then by going into the reports control source property you can select the new query with the dates and the date fields will be available in the field list, the other fields should work as long as then remained the same names.
Note: Experimenting with a duplicate database is your safest bet if your not sure.
For some reason I feel like this wasn't exactly what your looking for but maybe it will help you in the queries if you do it differently, You might want to clarify the dates because you said they are already used in queries and they originate in the table so I don't see why you can't use them in the report.
Ok enough Rambling for me,
Ziggy
