Seems we need to do some fixing here. We happen to have some exit numbers that are one off in this area.
18A -> 19
19 -> 20 (or 20A, see below)
20 -> I-276 (can't seem to find any 'posted' signage there)
This leads to some big problems. With '20' currently being for the I-276 interchange (& in use), we can't simply move it to it's 'correct' location. So, if we can find some good enough proof for '20' being @ I-276, I'd say keep it as 20, and correct '19' to '20A' to avoid breaking list files. Otherwise we could renumber current '20' to 'I-276', and still do the '19' tweak to '20A' I just mentioned.
Current 18A & 19 aren't in use right now, so 'correcting' them shouldn't cause any problems.