CDR identifier doesn't tell you the maximum overburn capacity - it simply states the maximum 'real' capacity of the disc. For 74 min CDs, this can be up to 74m50s. Overburning is burning past this point.
Typically you can overburn over 77 minutes onto a 74 min CD but the last couple of minutes are pretty dodgy in terms of quality. They can't always be read by by CD-ROM drives/stereos because the data is too close to the edge of the disc.