Speaking of unusual lead numbers —
When I first saw one like the Ruwe Hospital 4/8, I thought it actually had an extra-soft lead. A quick test proved that it didn’t. Obviously (in retrospect), a leading “2” was intentionally omitted on these pencils. This was apparently done so that the numbers in the fractions could be large and oriented in the same direction as was used for the 1, 2, etc. hardnesses.
But even when the style of the Blue Band changed and truncation of the numbers was no longer appropriate, it was initially retained —