I have done these kind of numbering systems in the past and truthfully, they are very difficult to do with native Quick Base.
An alternate suggestion is not to number sequentially, but rather use the [Record ID# in a formula.
For example
Right(ToText([Incoming year]),2)
& "-"
& ToText(Record ID#])
that would give a format like 17-123
You could also change it to ensure it had at least 4 digits like
17-0123
I know that is not what you asked for, but I have found its a real pain to get those kind of sub-numbering sequencing working. It can be done, with extra tables and look fields ands snapshots of summary totals, but it is not a 20 minute job to get working.