45′×45′ GTC OSIRIS z-band images of the fields of the all targets with the conventional direction (up is north and left is east). The blue dots are the object positions at the previous epochs published by other authors (Table 1), and the red ellipses are the projected positions where those targets are supposed to be on the dates of the observations in Table 2 according to their proper motions from the literature in Table 1. The two semi-axes of the ellipses show the errors of the proper motions in RA and Dec. WISE0004, WISE0013, WISE0301, WISE0422, WISE0833, ULAS1316, and WISE1553 were unambiguously detected within the error ellipses at their projected positions. However, for ULAS0926 and ULAS1319, we found that the proper motions given in the literature are overestimated; and for WISE2217, the proper motion is deviated. The red arrows indicate the positions at which the three sources should be. We recalculated their proper motions according to these positions and we listed the results in Table 3.