Apparently you are correct. The source I mentioned had indicated that the four fled Scotland together, but it appears that Douglass was earlier, according to the following free downloadable book from Google:
Historical Discourses, Relating to the First Presbyterian Church in Newark Jonathan French Stearns, D.D. - Newark (N.J.) - 1853 - 320 pages - page 86 footnote
“Dr. Macwhorter says, in his manuscript history, that Mr. Pierson, after his father’s death, ‘was for introducing more rigid Presbyterianism into Newark, in which he was encouraged by four men from Scotland, who had fled from the persecutions and troubles there under Charles II. Their names were Young, Nesbit, Clisby, and Douglass, who for their zeal and piety had been admitted by the first settlers to great privileges in the town. ‘… There is, furthermore, some apparent misapprehension in Dr. Macwhorter’s statement respecting the emigrants from Scotland. Excepting Douglass, none of the names mentioned appears in any list of settlers, or in any town transactions, until about the time of Mr. Pierson’s dismission. The name of Robert Young first appears in the records in 1690. James Clisby was admitted a planter in March, 1693-4. Dr. M.’s Century Sermon gives 1670 as the date of their arrival in Newark; but if they were here so soon, they certainly could not have been “admitted to great privileges in the town” until a much later day. None of their names, except that of Douglass, appear among the signers of the agreement to pay Mr. Pierson’s salary, when there was a difficulty respecting that matter in 1688. …’
Several publications from the mid-19th century, including the one I earlier referenced, repeated the apparent mistake that the four immigrated as a group.