#12 strength and #8 strength refers to the base charge of a detonator.

Historically detonators were made in a range of strengths, #6 for underground coal (Carrick Detonators) and #8 for initiating gelatin dynamite. With the change to less sensitive explosives a stronger detonator was required so ICI / Orica made a  #8* which is equivalent to a #12 strength DYNO detonator.

There were also #2, #3, #4 detonators but these were for testing the sensitivity of explosives and were not used for blasting.

The modern surface delays with low energy base charges probably relate to a #1 strength detonator.