The above transcript from the Burlington County Court on December 6, 1951 (his Honor Lester K. Drenk, presiding) states that

The prisoner was placed at the bar to plead and being charged, entered a plea of guilty thereto. The court sentenced him to be confined in the New Jersey State Prison for not less than 1 1/2 years nor more than 3 years on assault and battery and not less than one year nor more than three years on attempted escape. Both terms to run consecutively with each other and with the present one being served.

I suspect that the "one being served" was the one he'd been sent to Annandale for that January 12 on an indeterminate sentence. This is important to the overall story here, because it looks like he ended up doing time in an adult prison for that youth sentence. Ultimately, this is what got his December 6 conviction retroactively paroled in 1955.  

At the bottom of this page, another crime is mentioned: my dad, Frank Malvin, and Chester Farrell (with whom he had escaped Annandale) were indicted for assault & battery, but "on motion of the County Prosecutor the Court ordered this indictment nolle prossed (will not prosecute)." The fourth man mentioned in Indictment No. 24, Charles Ashdown, didn't even get on the court's docket. 

So I guess the prosecutors got the guy they wanted. The ringleader. The hoodlum.