ADAPT-WSA-derived instantaneous magnetic connectivity on 17 April 2021 at 16:00:00 UT for five of the spacecraft observing the SEP event, overlaid on the corresponding ADAPT-GONG map used to derive the coronal field, and the WSA-derived coronal holes (red is positive, blue is negative). The footpoint connectivity for each spacecraft is labeled with 12 colored points, one for each ADAPT-WSA realization, and the WSA-derived HCS is overplotted in yellow. The locations of two ARs that emerge on the solar far side are labeled with an “×,” yet are not incorporated into the ADAPT map until several days after this event. AR 12818, which is associated with a solar flare (discussed in Sect. 4), is labeled with an orange “×.” Orange shading marks the portion of the Sun not observed by remote imagers on board STEREO A, Solar Orbiter, or spacecraft near Earth.