Russell more often used the phrase "in present truth". Examples:
*** w09 3/15 pp. 83-84 Views From the Watch Tower ***
A brother in present truth had a peculiar experience lately. He was called to the house by cries of Fire! He found that the lighted lamp had fallen over on the bookstand. The oil was blazing over the little table, burning the books, etc.
*** w12 4/15 pp. 120-121 The Good Tidings Abroad ***
Our next appointment was at Berlin. There we met a very interested company of believers in present truth, some of whom had come about two hundred miles.
As already pointed out, "in the truth" was used once by Russell but it did not replace "in present truth" until the phrase "present truth" itself fell into general disuse.