According to Unitrade, only the SC 600ii March 17, 1972 perforated 11.0 x 11.0 original printing of this stamp should have the "Short $ Flaw". Neither the SC 599 (Perf 12.5x12.0) nor the SC 599a (perf 13.3 x 13.3) redrawn versions of SC 600 should have this variety.
The following is a SC 599a July 1977 perforated 13.3 x 13.3 redrawn version, but with the "Short $ Flaw". This stamp has been damaged through mailing and over time.


I have other examples where the top of the $ has been worn/scrapped off, but it is obvious that they were originally with a complete $ as the indented impression of the top vertical bar is there. In my example above, there is no evidence that there was originally a top to the $ sign - eg. no residual impression in the paper.
Any comments would be appreciated.