How Lucky Have You Gotten With Rush Tickets 1/2 Hours Before a Show?

Hey All - I am trying to determine if this is a viable strategy or if I have just gotten lucky. I am around ~20 minute walk to the Broadway theaters. Last week I noticed that TodayTix was still showing seats for the Gypsy evening performance so I went to the Box Office and got an awesome rush seat for $49 that was front mezz about an hour before the show. I similarly did this for Cult of Love before the holidays and got a "30 under 30" ticket from the box office an hour or two before the show. Are all box offices this flexible to sell rush tickets late in the day if they don't go in the initial rush line? There are a couple other shows I have my eye on (MHE, Death Becomes Her, Hadestown, & Juliet) that I would like to try to do this for.