Here are some threads where Pearce was discussed:

Shortstops

Centennial Commission

1902 Discussion Thread

1927 Ballot Discussion

1929 Ballot Discussion

1930 Ballot Discussion

Shortstop Positional Thread

All data are from Marshall Wright, The N.A.P.B.B.P. 1857-1870, directly or derived. I don't know what was published by contemporary guides, newspapers, even club records; how much was compiled or augmented by Wright, but I suppose that much of it was published then. One of his few explicit notes is attached to the Atlantic records for 1870: "As originally published, averages only included 21 professional games. They have all been adjusted to reflect all 36 professional games." This suggests to me that data without notes are directly from contemporary sources, but the suggestion is much too weak for comfort.

For 1870 only, the player-team-season records are games, base hits, and total bases on hits. For many of the 16 professional teams, not generally the strongest ones, we have those records for all games and separately for professional matches. Atlantic of Brooklyn is one of the clubs with two sets of records.

The Atlantics used a nearly set lineup especially in professional matches. Pitcher George Zettlein worked 33 of 36 pro and 13 of 22 other games. Shortstop Dickey Pearce worked 34 and 21. The other seven regulars worked all 36 pro and 18 to 22 other games.
The Atlantics made only one change from 1869, the first fully professional season, and the relative batting records of the nine were almost the same. Here they are listed in one order that roughly fits their relative batting records in both seasons. (Wright provides fielding positions but no batting positions.)

1870 Atlantics, professional games only (20-16)


Those are ranks among the nine regular players by Hits per game and Total Bases per game, and number of games.