The use of the word “potent” here reminds me of something you might see from the 19th century, e.g. “Doc McClure’s Potent Heart Tonic.” Maybe it’s the predecessor of today’s “extra strength”, but more likely it’s just a qualifying term associated with the science and industry of dyes (note the addition of “very” on the side of the box).
Like many brands of old copying pencils these come with point protectors, which must have saved countless shirts and pants from being ruined. The 745 is a blue pencil, but also came in red, purple, and green. The packaging indicates that they are suitable for hectograph work—a type of copying that was being done up to the 1960s. And hectographic pencils were said to contain a greater proportion of dye in their leads.
As late as 1990, Faber-Castell had two copying pencils in its catalog, the Noblot and the Blu-Blak, but I’m unaware of their differences. From what I’ve read it’s mainly artists and restorers anymore who look for indelible pencils, including tattoo artists who use hectographic pencils to transfer sketch designs on to the skin.
Here is an excellent article about the history of copying pencils.