Data, unlike agenda, remains the plural word that it is in Latin.

Unless firm data is available at an early date . . .

This is wrong. Is should be are.

If a singular is wanted, it is usually one of the data, not datum.

The ordinary meaning of datum is:

Any position or element in relation to which others are determined: chiefly in the phrases: datum point, a point assumed or used as a basis of reckoning, adjustment or the like—datum line a horizontal line from which heights and depths of points are reckoned, as in a railroad plan. . . . (Webster.)