When continuing down a Big Road column (Row 2 or lower, from Column 3 onward), Small Road applies Rule 2 by looking 2 columns to the left (`Column C - 2`). Under Case 1, if that reference column has a bead at the current row (`lastRow >= row`), Small Road records a Red (=) solid circle.
In `BBBBPBBBB...`, Column 1 has 4 Banker beads (`BBBB`), Column 2 has 1 Player bead (`P`), and Column 3 has 4 Banker beads (`BBBB`). As Column 3 descends through Row 2, Row 3, and Row 4, Small Road looks 2 columns back to Column 1 (ignoring Column 2 completely!). Because Column 1 has beads at Row 2, Row 3, and Row 4, all three marks on Small Road are Red (=) under Case 1.
Our locked road engine summarizes this exact mark in two steps: 1. Column 3 goes down to Row 2, so use Rule 2: look 2 columns back, at Column 1. 2. Column 1 has a bead at Row 2 too → red (=).