Copies of the original manuscripts are just as good as the originals themselves, provided one can discern the occasional errors of individual scribes and those manuscripts that perpetuated their errors. For example, if we have 1625 copies that contain Mark 7:16 and only 18 that omit it (only 5 of which predate the 10th century), then we can be pretty confident that a few early mss omitted the verse because it interrupted the lection that ran from Mark 7:14–24. The lection on the previous day runs from Mark 7:5–16 and ends with the verse in question. Also, the early versions support the verse's inclusion. Also, the verse doesn't have the earmarks of contamination from the lectionaries, which to my knowledge always have a completely different form of the words: ταυτα λεγων εφωνει ο εχων ωτα ακουειν ακουετω (cf. Matt 25:29; Luke 12:21; 13:9; 21:4), and always have only a few insignificant mss in support. On the other hand, this Mark 7:16 has the distinctively Markan expression ει τις εχει ωτα ακουειν ακουετω (Mark 4:23) as opposed to the form(s) used by Matthew and Luke (cf. Matt 11:15; 13:9, 43; Luke 8:8; 14:35). All this points to the fact that we know what the originals contained based on the many 1600+ mss that have preserve the words perfectly to the letter for roughly two thousand years.