The values you see in cells and panes are formatted. They are pretty-printed versions of the raw, actual stored data, or have special treatment applied to certain values or operations (such as for integer or decimal types treating 0 and blank as the same, or for [Disc #] blank and 1 as the same).
A field has two forms of expression:
Raw: [field,0]
Formatted: [field,1] (the default)
MC uses the formatted version by default (so you can just enter [field]). So in the case of Disc #, both blank and 1 are treated as one and the same.